What Timber Is Best for Loft Extensions in the UK?
Thinking about a loft extension? We’re not surprised, it’s one of the most popular ways to create extra space without extending out, especially in towns and cities where garden space is usually quite limited.
When it comes to the build, timber takes centre stage. Whether it’s reinforcing your roof, adding floor joists, or framing new stud walls, getting the timber right is very important.
So, what kind of timber should you be using?
Let’s break it down.
Structural Timber: The Backbone of Your Loft
Here’s the thing: not all timber is suitable for structural work. That’s where graded timber comes in.
You’ll usually be looking at two options:
- C24
This is the stronger, denser choice. It can handle heavier loads and longer spans. It’s the one structural engineers tend to prefer, especially when strength and stability are priorities. It also has fewer knots, which reduces the risk of warping. - C16
A more economical option, often used where loads are lighter. It’s still structural timber and can absolutely be used in loft conversions. It just depends on what your build requires.
Rule of thumb? If in doubt, go to C24. The slight extra cost is usually worth the added strength and peace of mind.
Softwood: Reliable, Cost-Effective, and Builder-Friendly
Most of the time, you’ll be working with softwood. Spruce and pine are two of the most common choices. Why?
Because it’s strong enough for structural work, lightweight enough to handle on site, and more affordable than hardwood.
Plus, it’s easier to cut and fix. Builders like it because it just works.
Hardwoods, on the other hand, are more niche in this context. You might choose oak for a decorative beam or exposed feature, but they’re not typically used behind the plasterboard. They’re too heavy, too expensive, and often more than you really need for the job.
Learn more about the differences between hardwood and softwood here.
What Timber Flooring Works Best in Loft Extensions?
Flooring is a big part of any loft conversion. It’s not just about something to walk on. It’s a structural element, often sitting between new joists and insulation, and it needs to handle weight, sound, and sometimes moisture.
A few popular choices:
- P5 Moisture-Resistant Chipboard
This is probably the most widely used loft flooring material in the UK. It’s tongue and groove, easy to lay, and designed to resist moisture. That’s ideal for newly converted lofts where ventilation might not be perfect right away. It’s cost-effective and stable when properly installed. - Structural Plywood
A solid alternative, especially if you want a bit more strength and durability. It’s great where you expect heavy footfall or are installing heavy furniture upstairs. Some builders also prefer it for its better screw-holding strength. - OSB (Oriented Strand Board)
Less common in domestic lofts, but it can be used. OSB3 is suitable for structural flooring and holds up well under load. It’s a little rougher underfoot, so it’s often topped with a finished floor.
Timber floors in lofts also need to consider soundproofing and thermal insulation. Often, acoustic roll or rigid insulation is fitted between joists before the flooring goes down. If you’re planning a bedroom or office up there, this makes a huge difference in comfort and noise control.
And don’t forget access. If flooring is being laid before a staircase is in place, the board sizes and weight matter. Smaller, lighter panels can be easier to manage through loft hatches or tight spaces.
Engineered Timber: When Standard Isn’t Enough
Sometimes a standard beam won’t cut it. Maybe the span is too long. Maybe you’re tight on head height. Maybe you just want that extra bit of precision.
Enter engineered timber.
You’ve got a few options here:
- I-Joists
Light, strong, and great for new floor structures. You can run services like pipes and wires through the web, which makes life easier for the plumber and electrician. - LVL (Laminated Veneer Lumber)
Ideal for high-stress areas such as lintels or where you need extra strength in a small profile. - Glulam Beams
These are laminated layers of softwood bonded together. Very strong, very straight, and they look good too. Perfect for exposed structural elements.
If you’re working with an architect or structural engineer, there’s a good chance they’ll specify some of these in.
Do You Need Treated Timber?
In most lofts, the timber will be indoors and well protected. But that’s not always the case.
If there’s any risk of damp or poor ventilation, especially in older properties, pressure-treated timber is a smart move. It helps guard against rot and insect attack. Once it’s in place, you don’t want to be going back to replace it.
Better to be safe than sorry. If you’re unsure, ask your builder or supplier. It’s one of those details that’s easy to overlook but hard to fix later.
Local Supply Makes All the Difference
If you’re based in Essex or anywhere around the London edge, sourcing timber locally saves you time and hassle. There’s less waiting, fewer delivery issues, and if you run short halfway through the job, you’re not stuck waiting three days for another pack.
We supply timber from our Brentwood yard to builders and trades across the region. That includes Romford, Chelmsford, Epping, Basildon and beyond.
Need advice? Just ask. We talk to builders about this stuff every day and we’re happy to help you figure out what’s best for your project.
Wrapping up...
Loft extensions can be transformative. They add space, value, and a new dimension to your home. But the build is only as good as the materials you put into it, and timber is right at the core of that.
Choose the right grade. Make sure it’s suitable for its role. Consider the flooring just as carefully as the framework. And source it from someone who knows their stuff.
That’s half the battle won.
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