diff --git a/.eslintrc.js b/.eslintrc.js
index 4959b133a0..9ae51f9bc5 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -30,6 +30,24 @@ module.exports = {
 
             "quotes": "off",
             "no-extra-boolean-cast": "off",
+            "no-restricted-properties": [
+                "error",
+                ...buildRestrictedPropertiesOptions(
+                    ["window.innerHeight", "window.innerWidth", "window.visualViewport"],
+                    "Use UIStore to access window dimensions instead",
+                ),
+            ],
         },
     }],
 };
+
+function buildRestrictedPropertiesOptions(properties, message) {
+    return properties.map(prop => {
+        const [object, property] = prop.split(".");
+        return {
+            object,
+            property,
+            message,
+        };
+    });
+}
diff --git a/src/CountlyAnalytics.ts b/src/CountlyAnalytics.ts
index fd2e8fe7a4..aac53b188b 100644
--- a/src/CountlyAnalytics.ts
+++ b/src/CountlyAnalytics.ts
@@ -685,7 +685,9 @@ export default class CountlyAnalytics {
     }
 
     private getOrientation = (): Orientation => {
-        return window.innerWidth > window.innerHeight ? Orientation.Landscape : Orientation.Portrait;
+        return window.matchMedia("(orientation: landscape)").matches
+            ? Orientation.Landscape
+            : Orientation.Portrait
     };
 
     private reportOrientation = () => {
diff --git a/src/components/structures/ContextMenu.tsx b/src/components/structures/ContextMenu.tsx
index ad0f75e162..9d8665c176 100644
--- a/src/components/structures/ContextMenu.tsx
+++ b/src/components/structures/ContextMenu.tsx
@@ -23,6 +23,7 @@ import classNames from "classnames";
 import {Key} from "../../Keyboard";
 import {Writeable} from "../../@types/common";
 import {replaceableComponent} from "../../utils/replaceableComponent";
+import UIStore from "../../stores/UIStore";
 
 // Shamelessly ripped off Modal.js.  There's probably a better way
 // of doing reusable widgets like dialog boxes & menus where we go and
@@ -410,12 +411,12 @@ export const aboveLeftOf = (elementRect: DOMRect, chevronFace = ChevronFace.None
     const buttonBottom = elementRect.bottom + window.pageYOffset;
     const buttonTop = elementRect.top + window.pageYOffset;
     // Align the right edge of the menu to the right edge of the button
-    menuOptions.right = window.innerWidth - buttonRight;
+    menuOptions.right = UIStore.instance.windowWidth - buttonRight;
     // Align the menu vertically on whichever side of the button has more space available.
-    if (buttonBottom < window.innerHeight / 2) {
+    if (buttonBottom < UIStore.instance.windowHeight / 2) {
         menuOptions.top = buttonBottom + vPadding;
     } else {
-        menuOptions.bottom = (window.innerHeight - buttonTop) + vPadding;
+        menuOptions.bottom = (UIStore.instance.windowHeight - buttonTop) + vPadding;
     }
 
     return menuOptions;
@@ -430,12 +431,12 @@ export const alwaysAboveLeftOf = (elementRect: DOMRect, chevronFace = ChevronFac
     const buttonBottom = elementRect.bottom + window.pageYOffset;
     const buttonTop = elementRect.top + window.pageYOffset;
     // Align the right edge of the menu to the right edge of the button
-    menuOptions.right = window.innerWidth - buttonRight;
+    menuOptions.right = UIStore.instance.windowWidth - buttonRight;
     // Align the menu vertically on whichever side of the button has more space available.
-    if (buttonBottom < window.innerHeight / 2) {
+    if (buttonBottom < UIStore.instance.windowHeight / 2) {
         menuOptions.top = buttonBottom + vPadding;
     } else {
-        menuOptions.bottom = (window.innerHeight - buttonTop) + vPadding;
+        menuOptions.bottom = (UIStore.instance.windowHeight - buttonTop) + vPadding;
     }
 
     return menuOptions;
@@ -451,7 +452,7 @@ export const alwaysAboveRightOf = (elementRect: DOMRect, chevronFace = ChevronFa
     // Align the left edge of the menu to the left edge of the button
     menuOptions.left = buttonLeft;
     // Align the menu vertically above the menu
-    menuOptions.bottom = (window.innerHeight - buttonTop) + vPadding;
+    menuOptions.bottom = (UIStore.instance.windowHeight - buttonTop) + vPadding;
 
     return menuOptions;
 };
diff --git a/src/components/structures/LeftPanel.tsx b/src/components/structures/LeftPanel.tsx
index 7f9ef7516e..e929306940 100644
--- a/src/components/structures/LeftPanel.tsx
+++ b/src/components/structures/LeftPanel.tsx
@@ -43,6 +43,7 @@ import {replaceableComponent} from "../../utils/replaceableComponent";
 import {mediaFromMxc} from "../../customisations/Media";
 import SpaceStore, {UPDATE_SELECTED_SPACE} from "../../stores/SpaceStore";
 import { getKeyBindingsManager, RoomListAction } from "../../KeyBindingsManager";
+import UIStore from "../../stores/UIStore";
 
 interface IProps {
     isMinimized: boolean;
@@ -90,10 +91,6 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         this.groupFilterPanelWatcherRef = SettingsStore.watchSetting("TagPanel.enableTagPanel", null, () => {
             this.setState({showGroupFilterPanel: SettingsStore.getValue("TagPanel.enableTagPanel")});
         });
-
-        // We watch the middle panel because we don't actually get resized, the middle panel does.
-        // We listen to the noisy channel to avoid choppy reaction times.
-        this.props.resizeNotifier.on("middlePanelResizedNoisy", this.onResize);
     }
 
     public componentWillUnmount() {
@@ -103,7 +100,6 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         RoomListStore.instance.off(LISTS_UPDATE_EVENT, this.onBreadcrumbsUpdate);
         OwnProfileStore.instance.off(UPDATE_EVENT, this.onBackgroundImageUpdate);
         SpaceStore.instance.off(UPDATE_SELECTED_SPACE, this.updateActiveSpace);
-        this.props.resizeNotifier.off("middlePanelResizedNoisy", this.onResize);
     }
 
     private updateActiveSpace = (activeSpace: Room) => {
@@ -228,7 +224,8 @@ export default class LeftPanel extends React.Component<IProps, IState> {
                     header.classList.add("mx_RoomSublist_headerContainer_stickyBottom");
                 }
 
-                const offset = window.innerHeight - (list.parentElement.offsetTop + list.parentElement.offsetHeight);
+                const offset = UIStore.instance.windowHeight -
+                    (list.parentElement.offsetTop + list.parentElement.offsetHeight);
                 const newBottom = `${offset}px`;
                 if (header.style.bottom !== newBottom) {
                     header.style.bottom = newBottom;
@@ -281,11 +278,6 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         this.handleStickyHeaders(list);
     };
 
-    private onResize = () => {
-        if (!this.listContainerRef.current) return; // ignore: no headers to sticky
-        this.handleStickyHeaders(this.listContainerRef.current);
-    };
-
     private onFocus = (ev: React.FocusEvent) => {
         this.focusedElement = ev.target;
     };
@@ -420,7 +412,6 @@ export default class LeftPanel extends React.Component<IProps, IState> {
             onFocus={this.onFocus}
             onBlur={this.onBlur}
             isMinimized={this.props.isMinimized}
-            onResize={this.onResize}
             activeSpace={this.state.activeSpace}
         />;
 
@@ -454,7 +445,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
                             {roomList}
                         </div>
                     </div>
-                    { !this.props.isMinimized && <LeftPanelWidget onResize={this.onResize} /> }
+                    { !this.props.isMinimized && <LeftPanelWidget /> }
                 </aside>
             </div>
         );
diff --git a/src/components/structures/LeftPanelWidget.tsx b/src/components/structures/LeftPanelWidget.tsx
index e88af282ba..16142069c4 100644
--- a/src/components/structures/LeftPanelWidget.tsx
+++ b/src/components/structures/LeftPanelWidget.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, {useContext, useEffect, useMemo} from "react";
+import React, {useContext, useMemo} from "react";
 import {Resizable} from "re-resizable";
 import classNames from "classnames";
 
@@ -27,16 +27,13 @@ import WidgetUtils, {IWidgetEvent} from "../../utils/WidgetUtils";
 import {useAccountData} from "../../hooks/useAccountData";
 import AppTile from "../views/elements/AppTile";
 import {useSettingValue} from "../../hooks/useSettings";
-
-interface IProps {
-    onResize(): void;
-}
+import UIStore from "../../stores/UIStore";
 
 const MIN_HEIGHT = 100;
 const MAX_HEIGHT = 500; // or 50% of the window height
 const INITIAL_HEIGHT = 280;
 
-const LeftPanelWidget: React.FC<IProps> = ({ onResize }) => {
+const LeftPanelWidget: React.FC = () => {
     const cli = useContext(MatrixClientContext);
 
     const mWidgetsEvent = useAccountData<Record<string, IWidgetEvent>>(cli, "m.widgets");
@@ -56,7 +53,6 @@ const LeftPanelWidget: React.FC<IProps> = ({ onResize }) => {
 
     const [height, setHeight] = useLocalStorageState("left-panel-widget-height", INITIAL_HEIGHT);
     const [expanded, setExpanded] = useLocalStorageState("left-panel-widget-expanded", true);
-    useEffect(onResize, [expanded, onResize]);
 
     const [onFocus, isActive, ref] = useRovingTabIndex();
     const tabIndex = isActive ? 0 : -1;
@@ -68,8 +64,7 @@ const LeftPanelWidget: React.FC<IProps> = ({ onResize }) => {
         content = <Resizable
             size={{height} as any}
             minHeight={MIN_HEIGHT}
-            maxHeight={Math.min(window.innerHeight / 2, MAX_HEIGHT)}
-            onResize={onResize}
+            maxHeight={Math.min(UIStore.instance.windowHeight / 2, MAX_HEIGHT)}
             onResizeStop={(e, dir, ref, d) => {
                 setHeight(height + d.height);
             }}
diff --git a/src/components/structures/MatrixChat.tsx b/src/components/structures/MatrixChat.tsx
index 49386c5f65..c01437b313 100644
--- a/src/components/structures/MatrixChat.tsx
+++ b/src/components/structures/MatrixChat.tsx
@@ -87,6 +87,7 @@ import defaultDispatcher from "../../dispatcher/dispatcher";
 import SecurityCustomisations from "../../customisations/Security";
 
 import PerformanceMonitor, { PerformanceEntryNames } from "../../performance";
+import UIStore, { UI_EVENTS } from "../../stores/UIStore";
 
 /** constants for MatrixChat.state.view */
 export enum Views {
@@ -225,7 +226,6 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     firstSyncPromise: IDeferred<void>;
 
     private screenAfterLogin?: IScreen;
-    private windowWidth: number;
     private pageChanging: boolean;
     private tokenLogin?: boolean;
     private accountPassword?: string;
@@ -277,9 +277,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             }
         }
 
-        this.windowWidth = 10000;
-        this.handleResize();
-        window.addEventListener('resize', this.handleResize);
+        UIStore.instance.on(UI_EVENTS.Resize, this.handleResize);
 
         this.pageChanging = false;
 
@@ -436,7 +434,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         dis.unregister(this.dispatcherRef);
         this.themeWatcher.stop();
         this.fontWatcher.stop();
-        window.removeEventListener('resize', this.handleResize);
+        UIStore.destroy();
         this.state.resizeNotifier.removeListener("middlePanelResized", this.dispatchTimelineResize);
 
         if (this.accountPasswordTimer !== null) clearTimeout(this.accountPasswordTimer);
@@ -1820,18 +1818,17 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     }
 
     handleResize = () => {
-        const hideLhsThreshold = 1000;
-        const showLhsThreshold = 1000;
+        const LHS_THRESHOLD = 1000;
+        const width = UIStore.instance.windowWidth;
 
-        if (this.windowWidth > hideLhsThreshold && window.innerWidth <= hideLhsThreshold) {
+        if (width <= LHS_THRESHOLD && !this.state.collapseLhs) {
             dis.dispatch({ action: 'hide_left_panel' });
         }
-        if (this.windowWidth <= showLhsThreshold && window.innerWidth > showLhsThreshold) {
+        if (width > LHS_THRESHOLD && this.state.collapseLhs) {
             dis.dispatch({ action: 'show_left_panel' });
         }
 
         this.state.resizeNotifier.notifyWindowResized();
-        this.windowWidth = window.innerWidth;
     };
 
     private dispatchTimelineResize() {
diff --git a/src/components/structures/RoomView.tsx b/src/components/structures/RoomView.tsx
index 28bf4da04c..bed54cc8df 100644
--- a/src/components/structures/RoomView.tsx
+++ b/src/components/structures/RoomView.tsx
@@ -83,6 +83,7 @@ import { objectHasDiff } from "../../utils/objects";
 import SpaceRoomView from "./SpaceRoomView";
 import { IOpts } from "../../createRoom";
 import {replaceableComponent} from "../../utils/replaceableComponent";
+import UIStore from "../../stores/UIStore";
 
 const DEBUG = false;
 let debuglog = function(msg: string) {};
@@ -1586,7 +1587,7 @@ export default class RoomView extends React.Component<IProps, IState> {
         // a maxHeight on the underlying remote video tag.
 
         // header + footer + status + give us at least 120px of scrollback at all times.
-        let auxPanelMaxHeight = window.innerHeight -
+        let auxPanelMaxHeight = UIStore.instance.windowHeight -
                 (54 + // height of RoomHeader
                  36 + // height of the status area
                  51 + // minimum height of the message compmoser
diff --git a/src/components/views/directory/NetworkDropdown.tsx b/src/components/views/directory/NetworkDropdown.tsx
index 66b7321ce0..08787812f6 100644
--- a/src/components/views/directory/NetworkDropdown.tsx
+++ b/src/components/views/directory/NetworkDropdown.tsx
@@ -38,13 +38,14 @@ import withValidation from "../elements/Validation";
 import { SettingLevel } from "../../../settings/SettingLevel";
 import TextInputDialog from "../dialogs/TextInputDialog";
 import QuestionDialog from "../dialogs/QuestionDialog";
+import UIStore from "../../../stores/UIStore";
 
 export const ALL_ROOMS = Symbol("ALL_ROOMS");
 
 const SETTING_NAME = "room_directory_servers";
 
 const inPlaceOf = (elementRect: Pick<DOMRect, "right" | "top">) => ({
-    right: window.innerWidth - elementRect.right,
+    right: UIStore.instance.windowWidth - elementRect.right,
     top: elementRect.top,
     chevronOffset: 0,
     chevronFace: ChevronFace.None,
diff --git a/src/components/views/elements/EffectsOverlay.tsx b/src/components/views/elements/EffectsOverlay.tsx
index 7bed0222b0..00d9d147f1 100644
--- a/src/components/views/elements/EffectsOverlay.tsx
+++ b/src/components/views/elements/EffectsOverlay.tsx
@@ -17,7 +17,8 @@
 import React, { FunctionComponent, useEffect, useRef } from 'react';
 import dis from '../../../dispatcher/dispatcher';
 import ICanvasEffect from '../../../effects/ICanvasEffect';
-import {CHAT_EFFECTS} from '../../../effects'
+import { CHAT_EFFECTS } from '../../../effects'
+import UIStore, { UI_EVENTS } from "../../../stores/UIStore";
 
 interface IProps {
     roomWidth: number;
@@ -45,8 +46,8 @@ const EffectsOverlay: FunctionComponent<IProps> = ({ roomWidth }) => {
 
     useEffect(() => {
         const resize = () => {
-            if (canvasRef.current) {
-                canvasRef.current.height = window.innerHeight;
+            if (canvasRef.current && canvasRef.current?.height !== UIStore.instance.windowHeight) {
+                canvasRef.current.height = UIStore.instance.windowHeight;
             }
         };
         const onAction = (payload: { action: string }) => {
@@ -58,12 +59,12 @@ const EffectsOverlay: FunctionComponent<IProps> = ({ roomWidth }) => {
         }
         const dispatcherRef = dis.register(onAction);
         const canvas = canvasRef.current;
-        canvas.height = window.innerHeight;
-        window.addEventListener('resize', resize, true);
+        canvas.height = UIStore.instance.windowHeight;
+        UIStore.instance.on(UI_EVENTS.Resize, resize);
 
         return () => {
             dis.unregister(dispatcherRef);
-            window.removeEventListener('resize', resize);
+            UIStore.instance.off(UI_EVENTS.Resize, resize);
             // eslint-disable-next-line react-hooks/exhaustive-deps
             const currentEffects = effectsRef.current; // this is not a react node ref, warning can be safely ignored
             for (const effect in currentEffects) {
diff --git a/src/components/views/elements/Tooltip.tsx b/src/components/views/elements/Tooltip.tsx
index 062d26c852..7e9ce9745c 100644
--- a/src/components/views/elements/Tooltip.tsx
+++ b/src/components/views/elements/Tooltip.tsx
@@ -22,6 +22,7 @@ import React, {Component, CSSProperties} from 'react';
 import ReactDOM from 'react-dom';
 import classNames from 'classnames';
 import {replaceableComponent} from "../../../utils/replaceableComponent";
+import UIStore from "../../../stores/UIStore";
 
 const MIN_TOOLTIP_HEIGHT = 25;
 
@@ -97,15 +98,15 @@ export default class Tooltip extends React.Component<IProps> {
             // we need so that we're still centered.
             offset = Math.floor(parentBox.height - MIN_TOOLTIP_HEIGHT);
         }
-
+        const width = UIStore.instance.windowWidth;
         const baseTop = (parentBox.top - 2 + this.props.yOffset) + window.pageYOffset;
         const top = baseTop + offset;
-        const right = window.innerWidth - parentBox.right - window.pageXOffset - 16;
+        const right = width - parentBox.right - window.pageXOffset - 16;
         const left = parentBox.right + window.pageXOffset + 6;
         const horizontalCenter = parentBox.right - window.pageXOffset - (parentBox.width / 2);
         switch (this.props.alignment) {
             case Alignment.Natural:
-                if (parentBox.right > window.innerWidth / 2) {
+                if (parentBox.right > width / 2) {
                     style.right = right;
                     style.top = top;
                     break;
diff --git a/src/components/views/messages/TextualBody.js b/src/components/views/messages/TextualBody.js
index b963e741a1..dc644f1009 100644
--- a/src/components/views/messages/TextualBody.js
+++ b/src/components/views/messages/TextualBody.js
@@ -36,6 +36,7 @@ import {toRightOf} from "../../structures/ContextMenu";
 import {copyPlaintext} from "../../../utils/strings";
 import AccessibleTooltipButton from "../elements/AccessibleTooltipButton";
 import {replaceableComponent} from "../../../utils/replaceableComponent";
+import UIStore from "../../../stores/UIStore";
 
 @replaceableComponent("views.messages.TextualBody")
 export default class TextualBody extends React.Component {
@@ -143,7 +144,7 @@ export default class TextualBody extends React.Component {
     _addCodeExpansionButton(div, pre) {
         // Calculate how many percent does the pre element take up.
         // If it's less than 30% we don't add the expansion button.
-        const percentageOfViewport = pre.offsetHeight / window.innerHeight * 100;
+        const percentageOfViewport = pre.offsetHeight / UIStore.instance.windowHeight * 100;
         if (percentageOfViewport < 30) return;
 
         const button = document.createElement("span");
diff --git a/src/components/views/right_panel/RoomSummaryCard.tsx b/src/components/views/right_panel/RoomSummaryCard.tsx
index 88928290f4..937037f644 100644
--- a/src/components/views/right_panel/RoomSummaryCard.tsx
+++ b/src/components/views/right_panel/RoomSummaryCard.tsx
@@ -46,6 +46,7 @@ import WidgetContextMenu from "../context_menus/WidgetContextMenu";
 import {useRoomMemberCount} from "../../../hooks/useRoomMembers";
 import { Container, MAX_PINNED, WidgetLayoutStore } from "../../../stores/widgets/WidgetLayoutStore";
 import RoomName from "../elements/RoomName";
+import UIStore from "../../../stores/UIStore";
 
 interface IProps {
     room: Room;
@@ -116,8 +117,8 @@ const AppRow: React.FC<IAppRowProps> = ({ app, room }) => {
         const rect = handle.current.getBoundingClientRect();
         contextMenu = <WidgetContextMenu
             chevronFace={ChevronFace.None}
-            right={window.innerWidth - rect.right}
-            bottom={window.innerHeight - rect.top}
+            right={UIStore.instance.windowWidth - rect.right}
+            bottom={UIStore.instance.windowHeight - rect.top}
             onFinished={closeMenu}
             app={app}
         />;
diff --git a/src/components/views/right_panel/UserInfo.tsx b/src/components/views/right_panel/UserInfo.tsx
index 9798b282f6..6e56b9259b 100644
--- a/src/components/views/right_panel/UserInfo.tsx
+++ b/src/components/views/right_panel/UserInfo.tsx
@@ -66,6 +66,7 @@ import { SetRightPanelPhasePayload } from "../../../dispatcher/payloads/SetRight
 import RoomAvatar from "../avatars/RoomAvatar";
 import RoomName from "../elements/RoomName";
 import {mediaFromMxc} from "../../../customisations/Media";
+import UIStore from "../../../stores/UIStore";
 
 export interface IDevice {
     deviceId: string;
@@ -1448,8 +1449,8 @@ const UserInfoHeader: React.FC<{
                     <MemberAvatar
                         key={member.userId} // to instantly blank the avatar when UserInfo changes members
                         member={member}
-                        width={2 * 0.3 * window.innerHeight} // 2x@30vh
-                        height={2 * 0.3 * window.innerHeight} // 2x@30vh
+                        width={2 * 0.3 * UIStore.instance.windowHeight} // 2x@30vh
+                        height={2 * 0.3 * UIStore.instance.windowHeight} // 2x@30vh
                         resizeMethod="scale"
                         fallbackUserId={member.userId}
                         onClick={onMemberAvatarClick}
diff --git a/src/components/views/right_panel/WidgetCard.tsx b/src/components/views/right_panel/WidgetCard.tsx
index 56e522e206..d7493e0512 100644
--- a/src/components/views/right_panel/WidgetCard.tsx
+++ b/src/components/views/right_panel/WidgetCard.tsx
@@ -30,6 +30,7 @@ import { Action } from "../../../dispatcher/actions";
 import { ChevronFace, ContextMenuButton, useContextMenu } from "../../structures/ContextMenu";
 import WidgetContextMenu from "../context_menus/WidgetContextMenu";
 import { Container, WidgetLayoutStore } from "../../../stores/widgets/WidgetLayoutStore";
+import UIStore from "../../../stores/UIStore";
 
 interface IProps {
     room: Room;
@@ -65,7 +66,7 @@ const WidgetCard: React.FC<IProps> = ({ room, widgetId, onClose }) => {
         contextMenu = (
             <WidgetContextMenu
                 chevronFace={ChevronFace.None}
-                right={window.innerWidth - rect.right - 12}
+                right={UIStore.instance.windowWidth - rect.right - 12}
                 top={rect.bottom + 12}
                 onFinished={closeMenu}
                 app={app}
diff --git a/src/components/views/rooms/AppsDrawer.js b/src/components/views/rooms/AppsDrawer.js
index 3ef8d71682..693ec8bc80 100644
--- a/src/components/views/rooms/AppsDrawer.js
+++ b/src/components/views/rooms/AppsDrawer.js
@@ -36,6 +36,7 @@ import {Container, WidgetLayoutStore} from "../../../stores/widgets/WidgetLayout
 import {clamp, percentageOf, percentageWithin} from "../../../utils/numbers";
 import {useStateCallback} from "../../../hooks/useStateCallback";
 import {replaceableComponent} from "../../../utils/replaceableComponent";
+import UIStore from "../../../stores/UIStore";
 
 @replaceableComponent("views.rooms.AppsDrawer")
 export default class AppsDrawer extends React.Component {
@@ -290,7 +291,7 @@ const PersistentVResizer = ({
 
     // Arbitrary defaults to avoid NaN problems. 100 px or 3/4 of the visible window.
     if (!minHeight) minHeight = 100;
-    if (!maxHeight) maxHeight = (window.innerHeight / 4) * 3;
+    if (!maxHeight) maxHeight = (UIStore.instance.windowHeight / 4) * 3;
 
     // Convert from percentage to height. Note that the default height is 280px.
     if (defaultHeight) {
diff --git a/src/components/views/rooms/RoomList.tsx b/src/components/views/rooms/RoomList.tsx
index 7b0dadeca5..896021f918 100644
--- a/src/components/views/rooms/RoomList.tsx
+++ b/src/components/views/rooms/RoomList.tsx
@@ -55,7 +55,6 @@ interface IProps {
     onKeyDown: (ev: React.KeyboardEvent) => void;
     onFocus: (ev: React.FocusEvent) => void;
     onBlur: (ev: React.FocusEvent) => void;
-    onResize: () => void;
     resizeNotifier: ResizeNotifier;
     isMinimized: boolean;
     activeSpace: Room;
@@ -404,9 +403,7 @@ export default class RoomList extends React.PureComponent<IProps, IState> {
             const newSublists = objectWithOnly(newLists, newListIds);
             const sublists = objectShallowClone(newSublists, (k, v) => arrayFastClone(v));
 
-            this.setState({sublists, isNameFiltering}, () => {
-                this.props.onResize();
-            });
+            this.setState({sublists, isNameFiltering});
         }
     };
 
@@ -537,7 +534,6 @@ export default class RoomList extends React.PureComponent<IProps, IState> {
                     addRoomLabel={aesthetics.addRoomLabel ? _t(aesthetics.addRoomLabel) : aesthetics.addRoomLabel}
                     addRoomContextMenu={aesthetics.addRoomContextMenu}
                     isMinimized={this.props.isMinimized}
-                    onResize={this.props.onResize}
                     showSkeleton={showSkeleton}
                     extraTiles={extraTiles}
                     resizeNotifier={this.props.resizeNotifier}
diff --git a/src/components/views/rooms/RoomSublist.tsx b/src/components/views/rooms/RoomSublist.tsx
index f9881d33ae..74987b066a 100644
--- a/src/components/views/rooms/RoomSublist.tsx
+++ b/src/components/views/rooms/RoomSublist.tsx
@@ -74,7 +74,6 @@ interface IProps {
     addRoomLabel: string;
     isMinimized: boolean;
     tagId: TagID;
-    onResize: () => void;
     showSkeleton?: boolean;
     alwaysVisible?: boolean;
     resizeNotifier: ResizeNotifier;
@@ -473,7 +472,6 @@ export default class RoomSublist extends React.Component<IProps, IState> {
     private toggleCollapsed = () => {
         this.layout.isCollapsed = this.state.isExpanded;
         this.setState({isExpanded: !this.layout.isCollapsed});
-        setImmediate(() => this.props.onResize()); // needs to happen when the DOM is updated
     };
 
     private onHeaderKeyDown = (ev: React.KeyboardEvent) => {
diff --git a/src/components/views/rooms/Stickerpicker.js b/src/components/views/rooms/Stickerpicker.js
index 82e8cf640c..3d2300b83c 100644
--- a/src/components/views/rooms/Stickerpicker.js
+++ b/src/components/views/rooms/Stickerpicker.js
@@ -40,7 +40,7 @@ const STICKERPICKER_Z_INDEX = 3500;
 const PERSISTED_ELEMENT_KEY = "stickerPicker";
 
 @replaceableComponent("views.rooms.Stickerpicker")
-export default class Stickerpicker extends React.Component {
+export default class Stickerpicker extends React.PureComponent {
     static currentWidget;
 
     constructor(props) {
@@ -341,21 +341,27 @@ export default class Stickerpicker extends React.Component {
      * @param  {Event} ev Event that triggered the function call
      */
     _onHideStickersClick(ev) {
-        this.setState({showStickers: false});
+        if (this.state.showStickers) {
+            this.setState({showStickers: false});
+        }
     }
 
     /**
      * Called when the window is resized
      */
     _onResize() {
-        this.setState({showStickers: false});
+        if (this.state.showStickers) {
+            this.setState({showStickers: false});
+        }
     }
 
     /**
      * The stickers picker was hidden
      */
     _onFinished() {
-        this.setState({showStickers: false});
+        if (this.state.showStickers) {
+            this.setState({showStickers: false});
+        }
     }
 
     /**
diff --git a/src/stores/UIStore.ts b/src/stores/UIStore.ts
new file mode 100644
index 0000000000..e7f6070627
--- /dev/null
+++ b/src/stores/UIStore.ts
@@ -0,0 +1,73 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import EventEmitter from "events";
+import ResizeObserver from 'resize-observer-polyfill';
+import ResizeObserverEntry from 'resize-observer-polyfill/src/ResizeObserverEntry';
+
+export enum UI_EVENTS {
+    Resize = "resize"
+}
+
+export type ResizeObserverCallbackFunction = (entries: ResizeObserverEntry[]) => void;
+
+
+export default class UIStore extends EventEmitter {
+    private static _instance: UIStore = null;
+
+    private resizeObserver: ResizeObserver;
+
+    public windowWidth: number;
+    public windowHeight: number;
+
+    constructor() {
+        super();
+
+        // eslint-disable-next-line no-restricted-properties
+        this.windowWidth = window.innerWidth;
+        // eslint-disable-next-line no-restricted-properties
+        this.windowHeight = window.innerHeight;
+
+        this.resizeObserver = new ResizeObserver(this.resizeObserverCallback);
+        this.resizeObserver.observe(document.body);
+    }
+
+    public static get instance(): UIStore {
+        if (!UIStore._instance) {
+            UIStore._instance = new UIStore();
+        }
+        return UIStore._instance;
+    }
+
+    public static destroy(): void {
+        if (UIStore._instance) {
+            UIStore._instance.resizeObserver.disconnect();
+            UIStore._instance.removeAllListeners();
+            UIStore._instance = null;
+        }
+    }
+
+    private resizeObserverCallback = (entries: ResizeObserverEntry[]) => {
+        const { width, height } = entries
+            .find(entry => entry.target === document.body)
+            .contentRect;
+
+        this.windowWidth = width;
+        this.windowHeight = height;
+
+        this.emit(UI_EVENTS.Resize, entries);
+    }
+}
diff --git a/src/utils/ResizeNotifier.js b/src/utils/ResizeNotifier.js
index fd12a454f6..4d46d10f6c 100644
--- a/src/utils/ResizeNotifier.js
+++ b/src/utils/ResizeNotifier.js
@@ -74,12 +74,6 @@ export default class ResizeNotifier extends EventEmitter {
 
     // can be called in quick succession
     notifyWindowResized() {
-        // no need to throttle this one,
-        // also it could make scrollbars appear for
-        // a split second when the room list manual layout is now
-        // taller than the available space
-        this.emit("leftPanelResized");
-
         this._updateMiddlePanel();
     }
 }