Loft area stripped to wooden frame showing wood posts and exposed wooden carcass

Lofts are such useful spaces in any home that it seems a real waste when they’re left without floors. If you’re planning to convert your loft into an extra, more useful storage space, or even into a complete, habitable space, then you’ll need to consider a number of things to make it safe and satisfy building regulations.


What type of wood is used for loft floor joists?


The type of wood used for floor joists is usually a certain dimensional lumber that’s made from regional softwoods. While hardwoods aren’t off the cards, softwoods tend to be cheaper, easier to work with, and account for movement due to temperature changes more effectively.


A common UK construction timber is redwood pine, but the type of wood used depends on the location: North America tends to use Douglas Fir, for example. Other common species are cedar and spruce.


What purpose will your loft be used for?


Loft conversion sitting room with exposed beams and central green sofa


Before deciding on the best timber for your floor, you need to know what the loft is going to be used for.


Most loft joists that are installed from the house’s original build are suitable to support light storage. But they’re frequently left un-topped. That is, the joists themselves are frequently left exposed, with the loft insulation visible between them. Putting anything, especially anything heavy, on the insulation is a surefire way to break through the plasterboard that’s holding the insulation up.


If you intend to just use your loft for light storage, then it’s usually suitable to cover the joists with sturdy, 10mm ply boards. But if you’re planning to use the loft for heavier storage, then you’ll usually need to add extra (and sometimes larger) joists to account for that weight. Adding extra 2x4 lengths or EWP joists usually suffices, but it’s worth consulting a structural engineer.


These extra joists can easily be ordered to your home or work site and be installed between the current ones, so you don’t need to worry about ripping everything out and can just shuffle the insulation around while installing. That said, be careful to cover up and wear suitable face masks while working with fibrous insulation as it’s significantly irritating to uncovered skin.


A more dramatic conversion, such as into extra rooms, will require structural calculations to account for joists that are able to bear the extra load of furniture, walls, and extra roof structures. For a conversion like this, you’ll usually need to work with a structural engineer to assess your particular needs. They’ll then be able to advise on the best joist materials, thicknesses, and amounts.


Covering the joists


Loft area stripped to carcass, showing exposed beams and no flooring


For a simple floor, ply boards are usually an affordable way to get a flat, strong, subfloor that can then easily be carpeted if necessary. The type of plywood available also ranges. You can get softwood ply, hardwood ply, marine, and birch. These each have their own desirable characteristics.


Softwood plys tend to be more affordable due to the fast growth of the trees, and they tend to be more flexible as a result. This flexibility can be a blessing or a curse depending on your requirements.


Hardwood ply sheets, on the other hand, are great for applications where rigidity is key. If you’re expecting to put lots of things with small pressure points (such as wardrobes with narrow feet or heavy beds) then a hardwood ply is great.


Marine and birch plys are for more specific applications. As its name suggests, marine ply is used in situations where moisture resistance is necessary. This tends to be things such as a sub-base for showers and wet rooms, but is also ok to use in most other settings – it just comes at a higher price due to the necessary treatment! Birch ply, while not necessarily water resistant, is often desirable for its strength and looks. It’s the distinctive light-coloured ply that’s frequently used for plywood furniture.


For full loft conversions, many folks prefer to finish their floors with hardwood floorboards that are laid at a right angle to the joists. In some cases, floorboards are the easier option even for storage floors as they can be easily passed up through loft hatches and then cut to length in situ.


Need advice?


The experts at your local Alsford Timber branch will be happy to advise if you’ve got a particular problem that needs solving. When you know what you need, easily order the materials online!