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Q&As
How do I make the ceiling joists in my loft deep enough to get building control approval?
I am hoping to floor the loft of our 1930s bungalow. To start with, I'm going to fit a loft ladder and use the space for storage, but with the option to add a staircase and windows for a useable room if funds allow in the future.
It has approximately 6" or 150mm deep ceiling joists. I understand I need at least 200mm. If I were to glue and screw the extra 50mm pieces on top of the existing joists, would this pass building control? Thanks.
One Answer
Hi David,
A caveat to start off: without seeing your loft space in person, there’s no way to ascertain the quality and structural stability of the current ceiling joists. So, the safest way to proceed would be to ask a structural engineer to take a look at your loft space and report on the suitability of the joists for what you’re planning.
In general, however, 150mm deep ceiling joists in good condition should be adequate to support loft boards and provide light storage from a structural point of view.
The bigger issue here might be insulation. Current Building Regs recommend 270mm of insulation in lofts. So, if you or a future owner wanted to achieve that level, you would need to increase the depth of the joists to accommodate it. Obviously, loft boards would get in the way of this.
Note that you shouldn’t squash insulation beneath loft boards, as compressing insulation dramatically reduces its performance.
There are various options for increasing loft joist depth to accomodate insulation. Traditionally, this was done by either cross-battening the joists with timber or affixing new timbers to the side of the joist, to raise the overall height. Modern options include products such as Loft Legs, which are basically small supports you can attach to the top of the joists and use as a support structure to lift the boards.
Hope this helps!
Chris Batesmith (Content Director, Build It)