Insulating loft Qq?

[nicam49]

Hi All! 2 questions actually... No, 3...Am about to re-lay loft insulation over a bathroom after a refit which included led downlighters. Can't get any info from supplier of downlighters if it's OK to insulate over the top of them, so assume it's not. Q1: can you get covers for the downlighters... Some old threads on here no.longer have working links. Q2; Is there any advantage in pasting aluminium foil to the plasterboard before laying down the insulation (to increase insulation properties)
Q3: the loft is boarded with 18mm chipboard, and each piece seems very heavy but suited my budget at the time (thinking of the joists taking the weight!) would plywood, say, 12mm be a lighter and just as strong an option?
Thanks for your thoughts!

 

[foxhole]

Hi All! 2 questions actually... No, 3...Am about to re-lay loft insulation over a bathroom after a refit which included led downlighters. Can't get any info from supplier of downlighters if it's OK to insulate over the top of them, so assume it's not. Q1: can you get covers for the downlighters... Some old threads on here no.longer have working links. Q2; Is there any advantage in pasting aluminium foil to the plasterboard before laying down the insulation (to increase insulation properties)
Q3: the loft is boarded with 18mm chipboard, and each piece seems very heavy but suited my budget at the time (thinking of the joists taking the weight!) would plywood, say, 12mm be a lighter and just as strong an option?
Thanks for your thoughts!

Are they fire rated down lights? 12mm ply is too thin.

 

[SFK]

there any advantage in pasting aluminium foil to the plasterboard before laying down the insulation (to increase insulation properties)

No thermal advantage.

can you get covers for the downlighters... S

See Google search here

https://www.google.com/search?q=downlight+covers&

 

[cdbe]

12mm ply is perfectly adequate for loft access and storage, but if it's over an average size bathroom, the joists are unlikely to have a large unsupported span so the extra weight of the existing chipboard shouldn't be an issue. Presumably you'll be raising it up to fit 300mm of insulation?

 

[nicam49]

Thanks Everyone for finding time to answer - very much appreciated.
Boards sit on 5 inch high standoffs I made from chipboard, (so not quite 300mm of insulation!)
I'll check if downlighters are firerated.. good point, hope they are.

 

[robinbanks]

No thermal advantage.

Strictly speaking it offers a microscopic improvement by lowering the emissivity of the surface, but it wouldn't be worth doing

would plywood, say, 12mm be a lighter and just as strong an option?

Are you concerned that the joists are right on the limit of what they can take, weight wise, and hence you need to reduce the weight of the floor because you're adding a weight of insulation?

 

[nicam49]

Hi Robin! Yes that's what I'm thinking - but more that I'm walking on it quite often - it's the highest central part of the loft and I walk on it to get to the lower roof section where I store my stuff.... and wondering about relieving it of some of the weight to minimise the risk of the ceiling joint opening up after I've repaired the crack. Thanks for replying. Sorry about the delay in answering!

 

[foxhole]

12mm ply is perfectly adequate for loft access and storage, but if it's over an average size bathroom, the joists are unlikely to have a large unsupported span so the extra weight of the existing chipboard shouldn't be an issue. Presumably you'll be raising it up to fit 300mm of insulation?

Been in a loft with 12mm ply floor , every step bowed the boards as you crossed .

 

[cdbe]

Been in a loft with 12mm ply floor , every step bowed the boards as you crossed .

It will, but what on earth difference does it make to anything?

My garage roof is EPDM on 9mm OSB decking, I'm 17 stone and the bowing when I walk on it is ridiculous - I reckon if I stood on one heel I'd go straight through it, certainly if I did a little jig, but I don't and I haven't - I dream of a 12mm ply deck, but the OSB cost me about £20.

 

[foxhole]

It will, but what on earth difference does it make to anything?

My garage roof is EPDM on 9mm OSB decking, I'm 17 stone and the bowing when I walk on it is ridiculous - I reckon if I stood on one heel I'd go straight through it, certainly if I did a little jig, but I don't and I haven't - I dream of a 12mm ply deck, but the OSB cost me about £20.

It’s called being unsafe .

 

[cdbe]

No it's not. It's probably a slight exaggeration to make a point (the reality is that I'm fully aware of the risk, and osb, even at 9mm will give loads of warning before it fails, the space between the rafters is barely 400mm and I couldn't fit through even if I tried).

The point is, that 12mm plywood is perfectly safe to use as loft flooring for access and storage, it's not a domestic floor and it makes no difference if it deflects a bit, it's beyond me why people drag 18 or 22mm chipboard up there, usually overloading their already overloaded ceiling joists.

 

[Deleted member 174758]

From having installed plywod diaphragm flooring I can tell you that even 9mm hardwood ply is pretty strong if adequately fixed to the joists. I thi k that is about as thin as I'd dare go

 

[robinbanks]

The

Hi Robin! Yes that's what I'm thinking - but more that I'm walking on it quite often

Ok, let's put some numbers to it.

An 18mm ply sheet is 28kg and it touches 7 joists.
Each joist, assuming bearing is even and none stick up more than others, thus carries about 4kg of ply
A 12mm sheet is about 18kg, so you're going to lighten the load on each joist by roughly 1.3kg

Your body weight bounding around up there is vastly more than this and is dynamically applied to various joists as you move.

Worst case, step on the line between boards and most your weight is going to be carried by the single joist under the gap.

Best case, step on the mid span, mid sheet and your weight is spread over the adjacent 4 to 6 joists with the inner ones taking more. The more the ply sheet flexes, the more of your weight is applied to the joists nearest your foot (if the ply sheet was perfectly inflexible your weight would distribute evenly across all touched joists)

Your weight moving around is going to have a considerably greater impact over whether the ceiling cracks (plaster isn't as flexible as wood) and the more you can spread that out to reduce the deflection, the less likely you crack the plaster

I'd leave the 18mm boards alone; I'd say the rigidity they offer is doing a better job of preventing cracking the ceiling than the 1.3 kilos extra they weigh contributes to your body weight. If the ceiling cracked with the 18mm boards, it wasn't because the boards were too heavy

 

[nicam49]

Thanks everybody! Your redone have been awesome! What a great forum this is.