Loft storage

[JJonesy]

I don't know if anyone can help me but I want to put some boarding down in my loft for storage. My house is around 10 years old and the joists are 35 cm by 80cm and they are laid 55 cm apart. Really worried about weight and just wondered if anyone knew if they would support the extra weight. :?

[stoneyboy]

JJonesy,
The boarding is not a problem but what you want to store will be. If you can try increasing the depth of the joists so you can add more insulation and strengthen the structure at the same time.
end

[The Riviera Kid]

This is something I'm interested in, as we're discussing our loft on another thread. Do the joists have to be totally replaced, or can additional high grade timber be bolted on top of the current joists (I also heard something about steel being screwed to the side)?

[stoneyboy]

The Riviera Kid,
If the existing structure will support it I would always recommend adding additional joists at right angles to the existing. This then allows space for services to be run in any direction.
end

[loftmonkey]

I'm in the same position as the original poster and can offer a bit advice to anyone thinking of converting the loft space for storage and putting down flooring. I've done a lot of research and consulted with a structural engineer so I know what's involved and things to watch out for.

Whilst it's normally fine to put down chipboard flooring and use the loft
as a storage space without needing to do anything else, the important thing to remember is that the loft joists are normally only intended to support the weight of the ceiling and roof and not much inbetween.

If you overload the joists by putting too much weight in one area, you will cause them to bend which will lead to cracking of the plasterboard ceiling below. In a worse case scenario you could cause one or more of the joists to crack if you really overloaded it.

Typically the joists in a loft will support about 40kg/m2 of weight so providing you're storing less than this you won't need to do any additional work to strengthen the joists. That may seem a lot, but when you take into account the weight of flooring, your own body weight and anything else you're storing up there, it doesn't take much to reach 40kg.

It's always a good idea to think about how you store stuff and spread the weight out over a larger area and always away from the middle of the joists (where they are likely to bend most).

If you plan on storing more than 40kg/m2 of weight up in the loft, or if you plan to use it as a work area, then you will probably need to strengthen the joists to prevent them from bending.

Providing you're not planning to have major weight in the loft and use it as a living space or gym etc, you can strengthen the joists by doubling them up, either by attaching additional joists to the existing ones, or by placing them inbetween.

If you're planning on anything other than basic storage, it's probably best to consult a structural engineer just to be safe as each case will be different and you may get away without needing any extra support or may need extra support, depending on your loft and requirements.

Hope that's useful as a basic guide..

Paul

[loftmonkey]

The Riviera Kid,
If the existing structure will support it I would always recommend adding additional joists at right angles to the existing. This then allows space for services to be run in any direction.
end

You have to bear in mind that although placing joists at right angles to the existing ones will help better distribute weight, it won't significantly strengthen the existing joists and stop them from bending in the middle.

If you want to strengthen the existing joists to prevent bending you need to double them up, either by placing joists alongside the existing ones and attaching them, or inbetween..that will effectively double the strength of the existing joists or halve the load on them.

Probably a good idea to do both, double up and put timber at right angles over the top or join new and old joists inbetween every foot or so.