cross batten in loft for additional insulation

richjamesw · 30 Oct 2009

i am in the process of converting my garage into a habitable room. One of the issues i have is in order to achieve the required insulation in the loft, i need on top of the 97mm of insulation between the truss rafters i will also need to put a further 150mm above it. As we are all aware we all need the roof space in order to store our rubbish that we will never use. Im thinking of cross battening over my trusses with 150x50 sw to raise the floor to enable the insualtion to go between and to be able to board over.
my only thought is the additional weight of the cross battening will have on the truss - second thoughts this is probably a fraction of the weight that 90% of us store in our loft these days. Any suggestions would be gratefull.

Agile · 30 Oct 2009

Only an idea! What about using 150 x 25 ?

Half the cost and it will be held vertical by the nails from the chipboard.

Still quite adequate for storage!

Tony

alittlerespect · 31 Oct 2009

Consider putting the insulation between the rafters, also if you use a PIR board you would not need such a thickness of insulation - around 80mm should more than satisfy your requirements.

Thinking aloud - you could cross batten the ceiling joists with 50 x 100 sawn softwood timber at 600 centres lay the insulation between the battens and complete with 18mm chipboard.

One word of caution - if you put the insulation over/between the joists the roof void is going to get extremely even unbearably cold in winter and it would end up costing you dearly to heat the roof space - so maybe go for the insulation between the rafters - just need to make sure you have around about 25mm gap between the insulation and the sarking felt.

Regards

seasickstevie · 1 Nov 2009

alittlerespect said:
... just need to make sure you have around about 25mm gap between the insulation and the sarking felt.

This is assuming you have felt. If it's an old roof with no felt, or a recent one with breathable material, I wouldn't bother to leave the 25mm.

Agile · 1 Nov 2009

alittlerespect said:
One word of caution - if you put the insulation over/between the joists the roof void is going to get extremely even unbearably cold in winter and it would end up costing you dearly to heat the roof space - so maybe go for the insulation between the rafters - just need to make sure you have around about 25mm gap between the insulation and the sarking felt.

Regards

I dont understand why you are thinking that a cold roof space is undesirable and needs to be heated ( after you have just added the insulation? )

My whole intention would be to save heating costs by keeping the heat in the house and out of the loft !

Tony

richjamesw · 1 Nov 2009

yes i mean on a pitched roof i would be insulating on the ceiling level, leaving the roof space cold. The idea seems good to do this but all this extra weight does it really have a desired impact on the truss?

seasickstevie · 1 Nov 2009

You say that you already have 97mm of insulation in place, but you don't say what kind of insulation it is.

If it were a high standard of PIR/PUR that was there already, I shouldn't think you would need to add a great deal to it.

If the stuff there isn't up to spec, then replace it with a higher performing insulation before adding extra thickness.

Agile · 1 Nov 2009

Yes, it does which is why I suggested 150 x 25 boards on their edge.

I would also use 12 mm chipboard as thats much lighter than 18 mm.

Hopefully you are not planning on storing heavy items?

Tony

Agile · 1 Nov 2009

A possibly cheaper solution would be to use 50-80 mm polystyrene with chipboard laid on top.

As long as you did not put too heavy weights on top it would probably take the weight by just resting on the joists.

Tony

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cross batten in loft for additional insulation

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