Loft Boarding - Insulation options

[pcmaniac]

Dear all,

Having read through the entire list of comments here I have gained some idea of what I think I should do, but thought I\\\'d try and get some confirmation from the list.

I have a number of computers that need to remain on 24/7/365 and would like to locate these in the loft. As a result, I will be getting a ring main installed. I also therefore need the loft to remain dry and at a relatively constant/comfortable temperature. This will NOT be used as habitable space, though.

I will be boarding out the loft using T&G chipboard (B&Q / Wickes) and am considering how best to insulate up there. The loft currently has about 2 inches of fibre matting over the lounge and bedrooms, but none over the kitchen, bathroom or hallway!

In order to maintain the temperature at a constant level, I am considering using ThermaWrap (double-sided foil backed bubblewrap, equivalent to 55mm polystyrene) attached to the rafters (max. 80mm space between exposed slate and bottom of rafters, no lining).

My question is this: Is it necessary / a good idea to top up the insulation between the joists and if so by how much? There is a total of 120mm depth available. Would I also need to strengthen the joists (currently 32mm thick, 120mm deep, spacing 420mm) to support the boards and possibly provide extra space for \\\"floor-level\\\" insulation?

Your thoughts or directions to where this information may be found will be much appreciated.

Regards,

PCmaniac

[Sponge]

I'd be very interested in some opinions too, as I am in a similar situation.

I've opted to keep the existing 6" of insulation inbetween the joists and I'm considering some of this stuff for inbetween the rafters and maybe on the side walls too.

[Sponge]

I've covered the ceiling with Thermawrap and I plan to batten over the Thermawrap before plasterboarding. Any advice on whether I should do it parallel or perpendicular to the rafters?

I was going to do it inline with them, but after a little Googling others have suggested doing it across.

[breezer]

can i mention that by putting insulation down on the loft floor you will insulate the house very well, but in doing so make the loft cooler.

what ever you do you must leave a ventilation gap so the roof itself can breathe

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[pcmaniac]

Thanks to everyone for their comments so far

breezer wrote:

can i mention that by putting insulation down on the loft floor you will insulate the house very well, but in doing so make the loft cooler.

This is probably the crux of the issue - I basically want a "warm loft", with fairly stable temperatures and humidity. At present, the loft is too warm, probably due to a combination of heat rising from below and the effect of the sun on the roof itself. Perhaps I shouldn't bother insulating the loft floor at all? Then again, I don't really want to have to rip up the boards after laying them if it turns out that I DO need floor insulation...!

breezer wrote:

what ever you do you must leave a ventilation gap so the roof itself can breathe

The roof is a slate roof with no lining/membrane underneath so is well ventilated through gaps between slates etc. However, as there is little depth in the rafters, insulating just between the rafters would provide little thermal benefit! Insulating the loft floor prior to boarding may therefore provide enough insulation for the habitable portion of the flat, with rafter insulation preventing large temperature/humidity variation in the roof space (the rafters are likely to be insulated using that foil-backed bubble-wrap stuff - e.g.ThermaWrap - "equivalent to 55mm polystyrene", whatever that means in R/U terms!).

I am already planning to cross-batten before laying the boards, but was just wondering whether the existing joists can take the weight of the boards+crossbattens+me+stuff... I really do NOT want the ceilings to start sagging / cracking after a few years!!

Any opinions?

[pcmaniac]

Sponge wrote:

I've covered the ceiling with Thermawrap and I plan to batten over the Thermawrap before plasterboarding. Any advice on whether I should do it parallel or perpendicular to the rafters? I was going to do it inline with them, but after a little Googling others have suggested doing it across.

I think this may be more of a personal preference / practicality issue - Cross-battens would provide more rigidity to the mounted plasterboard, reducing the chances and extent of any sagging in the future.
Inline battens may make it easier to fill the space with insulation.

Just my opinion! If it was me, I think I'd cross-batten.

[sm1thson]

hi pcmaniac i think i have come to the same conclusion as you for mine -cross battoning on the floor and thermowrap style stuff on the roof (i dont have felt either), so sounds like a good plan to me!