Raising Joist in Lofts

[sundew]

Hi, i want to board the our loft and need to raise the exsisting joists as we have numerous cables, etc running over the tops of the existing and some are differnet hieghts, etc. I'm going to use 4 X 2 timber but was wondering how to fix to the existing joists and should they run at right angles to the existing for added strength?

Thanks

 

[JohnD]

if you run them at right angles to the existing timbers, they will spread your weight while you are clambering about up there. If you screw them down tightly, and screw the boards on top, this will make the deck much more rigid, however it will not, as a whole, be any stronger so is not suitable for use as a loft conversion, or a habitable room, or for heavy items.

running counterbattens like this makes it easy to avoid cables, and also you can lay extra insulation between them.

You must not bury in insulation heavily loaded cables, like electric showers or immersion heaters. lighting circuits are very lightly loaded so are OK.

 

[Jetset]

PMFJI

I'm trying to do the same thing. The joists are 4x2 and there is 4" insulation between and 6" insulation at right angles (it's quite a recent job).

I'm trying to avoid placing too much weight on them but I don't want to compromise the insulation either. Would some more 4x2s at right angles squashing the insulation slightly be best or something smaller like 3x2 or even 2x2?

Jim

 

[JohnD]

insulation depends on its thickness. If you squash it you will reduce its effectiveness.

 

[Jetset]

Thanks for the reply John.

I'm actually less worried about the insulation than the weight of the deck. Do you think the 4x2s would be ok? That way, there would be minimal compressing of the insulation.

Jim

 

[JohnD]

it will not be strong enough for use as a habitable room or for storing heavy objects. Do not stand close together if there is more than one person in the loft.

You can keep your Christmas decorations up there with reasonable confidence though.

Counterbattening with more 4x2 will give you 8" of insuation, which is a reasonable amount (about 200mm) and the chipboard or ply will give a very slight amount.

However you should have an airspace between the insulation and the boarding to reduce the risk of condensation.

 

[Jetset]

John

Thanks very much for that. I'll give it a go and let you know how I get on. Probablly be a few weeks.

Many thanks.

Jim