Multiple root layouts with route groups in NextJS - Performance & Optimization

Performance: Multiple root layouts with route groups

MEDIUM IMPACT

This affects the initial page load speed and rendering performance by controlling how layouts and route groups are loaded and rendered.

Organizing routes with multiple root layouts and route groups to optimize loading

NextJS

app/(marketing)/layout.js
app/(marketing)/page.js
app/(dashboard)/layout.js
app/(dashboard)/page.js

// Using route groups with separate root layouts so only relevant layout code loads per route group.

Separates layout code by route groups, reducing bundle size and speeding up initial render.

📈 Performance GainSaves 50-100ms on LCP by loading smaller layout bundles.

Organizing routes with multiple root layouts and route groups to optimize loading

NextJS

app/layout.js
app/page.js
app/dashboard/layout.js
app/dashboard/page.js
app/settings/layout.js
app/settings/page.js

// All layouts are nested under a single root layout causing all layout code to load on every page.

All layout components load regardless of the route, increasing bundle size and delaying Largest Contentful Paint.

📉 Performance CostBlocks rendering for extra 100-200ms due to unnecessary layout code loading.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Single root layout for all routes	High (all layouts rendered)	Multiple reflows per page load	High paint cost due to large DOM	[X] Bad
Multiple root layouts with route groups	Low (only relevant layouts rendered)	Single reflow per route group	Lower paint cost with smaller DOM	[OK] Good

Rendering Pipeline

Multiple root layouts with route groups affect how the browser processes and paints the page by controlling which layout components are included in the render tree.

→Style Calculation

→Layout

→Paint

→Composite

⚠️ BottleneckLayout and Paint stages due to larger DOM and CSS from unnecessary layouts.

Core Web Vital Affected

LCP

This affects the initial page load speed and rendering performance by controlling how layouts and route groups are loaded and rendered.

Optimization Tips

1Use route groups to split layouts and reduce bundle size.

2Avoid nesting all routes under a single root layout to prevent loading unused code.

3Smaller layout bundles improve Largest Contentful Paint (LCP) and user experience.

Performance Quiz - 3 Questions

How do multiple root layouts with route groups affect the Largest Contentful Paint (LCP)?

A They reduce LCP by loading only necessary layout code per route group.

B They increase LCP by loading all layouts on every page.

C They have no effect on LCP.

D They delay LCP by adding extra network requests.

DevTools: Performance

How to check: Record a page load and inspect the Main thread for scripting and rendering times; check the Call Tree for layout and paint events.

What to look for: Look for reduced scripting and rendering times, fewer layout and paint events indicating optimized layout usage.