loft insulation guidance please

[muddyjames]

I have gone into my loft this weekend to board the centre section out to make it easier when I am up there. Down side to this is that I couldnt fit the double thickness of insulation down as it wouldnt compress thin enough. So the plan is to move the left over insulation to over the bedrooms which wil make them tripple insulated and insulate the roof trusses (the bits with the tiles above them) in the centre section mainly to compensate for the lack of insulation below.

I was going to buy pannels of polystyrene loft insulation that was half the thickness of wood so air can still get between the felt and polystyrene and put hard board up to hold the poly in place. Mum was talking to a friend the other day who said I should use thin boards that are covered in silver foil each side and lay them 90 degrees to the trusses. Which way is best?

It all looks like I may have a very very tiny leek in the loft too as the felt is wet and after last nights rain there is about a cm in size wet patch on the boards I laid yesterday. How much would it cost to get a bloke up there to have a look? It may just be a tile has slid down?

[Llanigraham]

There is a move against polystyrene insulation due to its fire problems. You can buy specific insulating panels but I can't remember their name. (something foreign)
Agreed, that if you are putting a lining up it is at right angles to the trusses.

Get the leak seen to first, what ever you do!

[discosteveo]

go to yr local builders mechant and ask for xtratherm its the good stuff, fire resistant ,high thermal rating and not itchy because its foam

oh some times they may tell you to try viagra when you ask for xtratherm HAHAHA????

[muddyjames]

xtratherm looks good but I cant find any prices though. I bet it isnt cheap. :-( they also show it running in the same direction as the trusses unlike advice given above. confused now.  :-k

[Range Rover Blues]

People run it across the trusses because it's easier that way, if you run it up and down then you need something to brace the joint as the rafters aren't often very thick.

I'd avoid anything that is a fire hazard though, a fire in the loft will go hellishly quick as I withnessed last half term when a house near the school burned down in just over an hour.  Started high up and whent through the loft.

TBH, once you have the loft boards down I think you'll find the loft is very cold anyway, I was looking at a protective/insulating treatment for the exterior but it's about 5 grand initially (pays beack in about 5 years) that would also sort out any leaks and prevents concrete tiles form absorbing waterm which is an issue with heavy snowfalls etc because the tiles get very heavy when they are wet.

[markppearson]

For your trusses, I used polythene sheeting to keep any chance moisture penetration out, then used foil backed 12.5mm gyproc (foil facing roof tiles) and taped it up and then painted over it.

For the flooring, the full thickness is a legal requirement except on new builds where possible.  25mm, boards would be best to give you stability and strength. If you want to compensate for the loss of insulation, then you could again use 12.5mm gyproc under the boards. These will also provide you with a bit of sound deadening if you are planning to use it a 'room'.

[carbore]

I recently had a lot of work done on my house and would say the following.

Insulation is the most cost effective (fastest retun on investment) way to save money/be green. Forget about ground source heating/solar etc unless you can wait 7-10 years. Good insulation is has a very quick payback, so what im saying is its worth investing in as much as you can afford (and then some).

Secondly, id never take any risks re fire safety as mentioned.

There are often grants for lof insultaition, but they come with strings attached, it may be worth looking around as much as possible to see if you can get some money towards it, but unfortunatley its usally schemes where people fit it for you, as opposed to DIY.

Thirdly, remember that Energey efficiency is part of the HIP (Home Inspection Pack) so again its worth doing properly to make your house better on this scale.

Im sure you only want to do this once, so take all advice going before proceeding.

Also re products, we used various including a silver blacket type thing that went in the studwork. better than traditional fibregalss wool.

[winchman]

I was going to buy pannels of polystyrene loft insulation that was half the thickness of wood so air can still get between the felt and polystyrene and put hard board up to hold the poly in place. Mum was talking to a friend the other day who said I should use thin boards that are covered in silver foil each side and lay them 90 degrees to the trusses. Which way is best?

Stop now!!
If you insulate the loft floor and the bit under the felt you may get condensation under the felt.
I know I have done this but only got a small bit done before we found the problem.
I will post more detail later when I have more time

[T30CDB]

Not wanting to throw a spanner in the works but firstly what size are your ceiling joists ( the emphasise is on the word ceiling not floor joists ) as older houses only had sufficient sized timbers to carry the weight of the ceiling not a floor. If you wish to add extra insulation in between the ceiling joists and then board it i would recommend enhancing the existing ceiling joists with another timber of equal thickness to provide extra strength and ensure that it gets as close as you can to the external wall plate as possible and fixed to the jack rafter as well as finishing on top of any structural walls. so if you only have 3 inch x 2 inch or 75mm x 50mm timbers these will definitely need doubling up. Don't nail your boards down as any electrician in the future that needs to get them up will curse you for ever and a day.

[muddyjames]

I have a mid 90's built house. I did think about the weight but there used to be a water tank but that was removed when the combi boiler got installed. also my house isnt very big either so the stud work in my 2 walls up stairs are about a 1.3 of thr way in from each end of the house giving some support to the ceiling joists. I know they arent supposed too but not a huge amount of weight has been added with the removal of the water tank.

So if I dont insuklate the rafter space then, can I just board it over with hard board to keep drafts out and to act a bit like insulation but not? I only want to board out the top half of the trusses.

cheers

james

[redhand]

First don't use plastic sheeting to line the roof it will cause condensation. Think solar stills. I use foil backed bubblewrap (Screwfix) or celotex if I'm insulating roofs. But the previous post re increasing the depth of the joist is probably the best idea. fix them at right angles to the existing joists and  insulate between them with ordinary rockwool insulation.

[winchman]

The problem here is there is a load of science to roof construction.
But most of us choose to ignore it.
Weight
The roof is designed to hold the weight of the tiles / slates I would imagine a couple of ton spread over the total area + a factor for a coat of heavy snow + a bit.
The other very important thing is the construction.
My 1960s roof is called a Cold roof and as such has tiles with a water proof membrain under it incase any tiles should leak ( just like roofing felt.
The problems start when you mess with the insulation, in 99% of cases its fine to just fill the gaps between the joists with any insullation you like, but the roof will still be vented as per the builder designed it so alls well.
If you insulate the slopy bit you will stop this natural ventillation and as I did get some condensation which is possibly the last thing you want as a nice dry loft is now damp and wet.
My advise would be insulate the gaps between the joists on top of the ceiling with rockwool as its cheap, if you are going to board the loft for storage get a set of calcs done just to prove the beams ar capable of taking the weight of the boards and any junk you put up there.
Draughts, the roof is desinged to have these as ventillation, you can get more benifit buy putting 6" of insulation above the ceiling as the draughts wont matter as they wont blow in to the house.

[T30CDB]

With out be patronising or questioning your knowledge in any way , when you say trusses i take it you have one or two diagonal timbers coming from the roof timbers down to the ceiling timbers acting as braces. If this is the case and you have walls as you say supporting underneath you shouldnt have too much trouble boarding out a bit of floor to store light things on. no engines,axles or chassis though. As for insulating in between the trusses on the slope you would have to ensure you maintain an flow underneath the black felt otherwise this will form a cold bridge and cause condensation as previous posts mention. best bet is to insulate the ceiling and put an extra jumper on when you go up there

[muddyjames]

With out be patronising or questioning your knowledge in any way , when you say trusses i take it you have one or two diagonal timbers coming from the roof timbers down to the ceiling timbers acting as braces.

my knowledge is VERY poor on roof vocabulary! I am meaning the timber that holds the roof up from front to house to middle and back down to back of house. Also where the felt touches and the tiles sit on.

If this is the case and you have walls as you say supporting underneath you shouldnt have too much trouble boarding out a bit of floor to store light things on. no engines,axles or chassis though. As for insulating in between the trusses on the slope you would have to ensure you maintain an flow underneath the black felt otherwise this will form a cold bridge and cause condensation as previous posts mention. best bet is to insulate the ceiling and put an extra jumper on when you go up there

This is why I was thinking about putting polystyrene in there half the thickness of the trusses so when I put hard board onto the trusses the polystyrene sheets fell onto it there for leaving a gap for air to flow and as I want to only insulate the top half of the roof the rest would be open to the loft.

[redhand]

The foil backed bubblewrap is designed to be stapled across the roof spars. and thus still allowing proper ventilation of the roof. It is I believe equivalent to 4" of rockwool. 

[muddysteve]

just dont put polystyrene anywhere near your electrical cables as it will make the insulation fall off them, just stick some rockwool in and nail some boards ontop "simples"

[Mikieb1981]

have done this recently as part of a loft conversion which meets building control

Insulation of 100mm between the trusses use either celotex or similar,then insulation of 25mm over the top of the trusses, again celotex or similar, followed by plasterboard over the top.

You can use insulated plasterboard and do away with the 25mm insulation but its v expensive

A 50mm air gap must be maintained behind the 100mm insulation and the roof should have vented soffits and vented ridge tiles fitted.

There is a set u value which has to be met for it to comply with building control to be living accomodation and only the celotex or similar foil backed foam insulations will meet this.

If its not for living space then use rockwool as its lots cheaper, you can buy rockwool for cavity wall insulation that is denser than the normal stuff used for lofts, its a bit dearer but it will be easy to hold in place with string and hardboard over the top.
All depends what its used for and if you want to have it as living space should you ever sell the house.

[winchman]

Quote
best bet is to insulate the ceiling and put an extra jumper on when you go up there
Quote
Thats the best thing to do, its cheap and will give you some storage.
I did all the proper things and still got condensation troubles so I would just do the above unless you are going fro a builder to do a proper full conversion

[jay2578]

rockwool under the intended floor, celotex or kingspan boards(available in varying thicknesses) between trusses, maintaining an air gap between it and the felt. celotex and kingspan are cut with an old handsaw to a mm or two oversize and wedge in. no need for hardboard. if you need any more info/ guidance pm me and i`ll email you some drawings as i do this sort of thing all the time 

[muddyjames]

cheers for the info. Waiting until next month to look at my bank and see if I have spare cash!