Another Loft Insulation/Floring Question!

[adsloft]

Hello everyone, this is my first post so please go easy on me!!

I am after some advice, having suffered with condensation issues in my loft, like a lot of people, I am attempting to improve things. I currently have 100mm of loft insulation between the floor joists but want to increase this to the recommended 270mm in an attempt to make the home more efficient and possible assist with the condensation issue. I will obviously ensure the air flow gaps are correct, I have a feeling the existing insulation needs to be cut back a little before I lay the extra stuff. I also want to floor some of the loft to allow for storage, my plan is to fit some additional timber, 7x2, at 90degs to the existing floor joists so I can lay the extra insulation in the between and then floor on top. Can anyone advise me on the best method to attach the timber to the existing joists? Also any other advice would be gratefully received! Cheers!

 

[PaulJR]

I would not recommend laying the 7"x2" joists as you describe, they will bear directly onto the ceiling joists and your floor is going to end up being supported by the ceiling. This will crack your ceiling etc.

Take a piccy of your loft and some measurements, you need to have the new floor span clear over the ceiling, and only be supported at its ends.

 

[adsloft]

Thanks for the reply, what your saying makes sense, are you suggesting though that I should be fixing the new joists to the house wall? Also I have had a bit of a wobble about using 7x2, it is going to weigh a lot (have worked out I need about 18ms of timber) so thinking now about using 2x2 timber but increase the height to the 170mm from existing joists by making upstands also from the 2x2, does that sound like a reasonable option?

 

[PaulJR]

The new joist should fix to a wall really. This keeps the floor independent of the ceiling - if you load the ceiling it will sag under the weight and crack your plaster - or worse!

If you are only going to use it for light storage, then you can add joists over the top of the others, but they dont act together so you have the same issues.

A better, but expensive option is to insulate between the rafters (sloping roof timbers) with celotex or kingspan PIR. Dont use polystyrene - to risky in a fire. You can then lay boards over your ceiling joists - but it wont take a lot of weight.

7"x2" joists will span 4250 at 400mm centres as a floor - what are your loft dimensions?

 

[adsloft]

The plan is to only floor the centre section of the loft as it is awkward to get to the out side edges. The other issue I have is that I am flooring around the hatch and the water tank/header tank so cannot do continuos runs from one wall to the other. It measures 4.5m from from side to the other and is about 4m wide (the area to be floored that is!

 

[PaulJR]

Then either;

use larger joists as spacer fixed on top of the ceiling joists and get your insulation thickness under the boards, but remember not to go mad with the amount of stuff you put up there

or, insulate between rafters and board the existing joists - but only for lightweight storage etc.