Loft joist strengthening

[edc]

Hi everyone,

I've trawled through all the loft boarding posts on this forum, and whilst I've managed to pick up quite a lot I'm still very confused about my situation. If anyone can help with the below I would be very grateful!

I'm trying to improve the insulation in my loft (house is a ~1900 mid terrace) and board it out with 18mm chipboard for storage only (stress no conversion). I'm concerned about whether the joists are capable of taking the additional weight (of the board, plus junk, plus someone walking around) as they're only 4x2s and about 3.6m span spaced every 14ins or so.

Current situation:

The diagonals in green are not on each joist - just one at either end and one in the centre (ie. at the top, middle and bottom on the plan view below).

All timber is 4x2 and insulation is laid throughout to 100mm. I'm looking to up that to approximately 250mm.

I've read about laying batterns at 90 to the existing joists, which would increase the height to lay the insulation, but will this do anything to strength the floor?

I've also ready about increasing the thickness of the joists by adding timber to the tops of the existing joists, or running additional timber in parallel.

Whats the best approach, or is it a combination of the two?

Thanks in advance for any answers!

Ed
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[JohnD]

cross-battening helps spread the load across several timbers but does not increase overall strength. If the battens and boards are all screwed down tightly they make the "floor" a lot more rigid. which will help while you are clambering about, but will not enable to to store your grand piano up there.

Ply is stronger and more rigid than chipboard. Larger pieces add more rigidity than little panels. I can just get an 8x2 into my loft.

You can lay more insulation between the battens. As it will be at right-angles to your existing insulation it will tend not to have the same gaps and cold spots.

You can also position your battens to protect pipes and cables.

do not bury cables in insulation (except lighting cables, which are very lightly loaded)

 

[edc]

Thanks for your reply JohnD.

It sounds like cross battening is the way to go, although I am still concerned that a 4x2 timber seem quite small to take the weight over a 3.6m span, even if the cross battening does spread it out over multiple joists. Is there an easy/non-invasive/cheap way of adding to the joists to improve the overall strength?

Lofts tend to "eat" junk, and whilst I know that the grand piano will never make it up there, I don't want to end up with cracks all over the ceiling once I've finished decorating! I guess I'm just looking for some way of improving the situation now so I dont have to empty the loft and unscrew the floor in a few years time!

I've already got a large quantity of 8x2 chipboard panels from another "project", so they're going have to stick as the base! Good news is that I can get a full panel in through the hatch however!