Wall Framing & Structural Design for a DIY Garden Room

Wall framing is where a garden room really starts to feel like a building rather than a project on paper. Get this stage right and everything that follows (roofing, insulation, cladding, windows and doors) becomes easier, straighter, and far more durable.

In this article, I’ll focus on the wall framing system I use in my own garden room builds: 100×47mm C16 structural timber, with box steel lintels for wider openings. This approach strikes a good balance between strength, simplicity, cost, and ease of construction for DIY builders.

Why Wall Framing Matters More Than You Think

Garden room walls don’t just hold up the roof. They:

• Transfer roof loads down into the base
• Resist wind loads and racking
• Support doors, windows, and cladding systems
• Define insulation thickness and internal finishes

In my recent garden room build, the walls were doing all of the above, supporting a cold flat roof, large glazed openings, and full-height cladding, while still being built entirely on site with basic tools.

Further reading: What’s the difference between cold and warm roof construction?

My Go-To Wall Framing Timber: 100×47mm C16

For almost all of my garden room projects, I use 100×47mm C16 construction timber for wall framing. (95x45mm actual size)

Why 100×47mm?

• Structural strength: More than adequate for single-storey garden rooms
• Insulation-friendly: Allows for meaningful insulation thickness – 90mm or a combination of 50mm PIR and 40mm wool.
• Stiffness: Reduces wall flex compared to thinner CLS
• Availability: Easy to source and consistent in size

C16 is absolutely sufficient here. While C24 is stronger on paper, for garden room walls, it’s usually unnecessary. C24 should be considered for floors and roof construction, where support spans are wider.

Stud Spacing: Keeping It Simple and Strong

I typically space wall studs at 400mm centres. Some may consider 600mm centres, but in practice, I’ve found 400mm gives:

• Stiffer walls
• Better resistance to racking
• Easier fixing for OSB and plasterboard
• Cleaner support around openings

In one build where the garden room was slightly exposed to prevailing winds, the tighter stud spacing made a noticeable difference once the structure was up. It felt solid even before sheathing went on.

Understanding Loads

Garden room wall loads are generally modest, but they still need to be respected.

Typical loads walls are supporting:

• Roof dead load (timber, insulation, roof deck)
• Roof live load (snow, maintenance)
• Wind loads acting on the walls and roof
• Point loads around openings

Using 100×47mm studs at 400mm centres, combined with structural sheathing, easily handles these loads for typical garden room sizes, particularly when paired with sensible roof spans (covered in more detail in my roof construction guides).

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Framing Door & Window Openings

This is where wall framing often goes wrong on DIY builds. The opening accuracy is essential to ensure windows and doors fit securely. It’s important to order your windows and doors before construction of the openings. A 10mm addition should be added to each edge to allow for alignment and packing, which ensures the frames can be squared up evenly. This allows for smooth opening and closing once installed.

Standard Openings

For normal doors and windows:

• Full-height studs either side
• Double studs where openings are close together
• A timber lintel built from doubled 100×47mm timbers for smaller spans

This works well for openings up to around 1.2–1.5m, depending on roof loads.

Using Box Steel for Wide Openings

For larger openings, especially bi-folding doors, timber lintels quickly become bulky. The spans force the need for thicker lintels, which impacts the height of the garden room.

In my recent garden room build, I used box steel to span a wide glazed opening. This allowed me to:

• Keep wall depth consistent
• Avoid oversized timber beams
• Maximise head height internally
• Maintain clean lines externally

The above image illustrates in detail a typical front wall with a large 3m opening for a bi-folding door. The box steel lintel ensures the heavy roof is supported without affecting the operation of smooth door opening and closing. The box steel lintel is supported by a strong timber support on either side. Noggins are used to prevent the bowing or twisting of the vertical timbers. Once the box steel has been insulated and boarded, it disappears entirely. Wool insulation can be used within the box.

If you’re planning large openings, this is one area where steel is well worth considering, and often simpler than trying to engineer complex timber solutions.

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Fixing the Wall Frame to the Floor/Base

Securing the wall frame to the base is critical to the strength, stability, and longevity of a garden room. This connection transfers roof loads, wind loads, and uplift forces safely into the ground.

Always use a sole plate with a DPC layer between the wall frame and the base, whether you’re building on timber or concrete. This prevents moisture from being drawn into the structure and protects the framing long-term.

On a timber base, fix the walls through the sole plate directly into the base joists using heavy-duty structural screws. Wherever possible, align wall studs with joists below so loads transfer cleanly through the structure. Avoid fixing walls only to the floor decking.

If you’re building a timber base, I cover this in detail here:
How to Build a Timber-Framed Garden Room Base

On a concrete base, secure walls using anchor bolts or high-quality masonry fixings, positioned close to stud locations. Fixings should be evenly spaced and tightened gradually to keep walls plumb and avoid crushing the timber.

If you’re building a concrete base, I cover this in detail here:
How to Build a Concrete Garden Room Base

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Preventing Racking & Adding Strength

Walls don’t just carry vertical loads; they also resist sideways forces.

In every garden room I build, wall frames are stiffened using structural sheathing (typically 9 or 18mm OSB) fixed to the outside of the studs. This:

• Prevents racking
• Locks the structure square
• Provides a solid fixing layer for battens and cladding

Once sheathing is installed, the transformation is immediate. The building goes from flexible to rock-solid.

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Thinking Ahead: Insulation & Services

While insulation is covered in detail in a separate article, wall framing sets the rules.

Using 100×47mm studs allows:

• Good insulation thickness
• Space for services without excessive notching
• Reduced cold bridging

In my builds, I always think ahead to:

• Electrical routes
• Vapour control layers
• Internal linings

Getting this right at framing stage avoids compromises later.

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How This Fits with the Rest of the Build

Wall framing doesn’t exist in isolation. It ties directly into:

• Roof design and load paths
• Insulation and vapour control strategy
• Window and door detailing
• External cladding systems

If you’re still at the planning stage, I’d strongly recommend reading:

How to Test Soil and Ground Conditions Before Building a Garden Room
Do You Need Planning Permission for a Garden Room? The Definitive Guide

These early decisions influence wall design more than most people realise.

Final Thoughts

You don’t need complicated structural calculations or exotic materials to build strong, durable garden room walls.

By sticking to:

• 100×47mm C16 framing
• 400mm stud spacing
• Steel lintels where openings demand it
• Proper fixing to the base
• Structural sheathing

you’ll end up with walls that are straight, strong, and ready to support everything that comes next.

This is the same approach I use in my own garden room builds, proven, repeatable, and well-suited to DIY construction.