Layout in the loft : What's the best way of insulating the roofspace?

Basically, what you want to do is insulate the underside of the actual tiles or slates, and that can be done by plating the underside of the rafters with plasterboard or insulation board. However, you have to ensure that you provide for a fair amount of ventilation between the plating and the tiles/slates to prevent the possibility of dry rot. So it is worth involving a good builder to make sure that the insulation is done properly.

If you have the space, a better way is to build a room in the loft space so that you get a level of heat insulation, but still leave plenty of ventilation/circulation area in the voids between the underside of the roof and the walls and ceiling of the room.

The last thing you want to do is to create areas in your roof space where there is little or no natural ventilation. It is one area in the house where you can get dampness for several kinds of reasons - leaky roof, wind in wrong direction, wrong kind of snow, etc., - and any dampness should be able to dry off quickly with ventilation.

And for any work in the loft, you have to watch out for the loading on the joists. If your house is a modern one, it's a fair bet that you are going to have to provide some strengthening of the joists unless you want to make surprise visits to the rooms below :-)

Jim.

If you can, use 2 layers of 25mm Celotex or Kingspan. Place one layer between the rafters leaving an air gap between the Celotex and the underside of the roofing felt. Then place the other layer across the rafters. Should give insulation equivalent to a cavity wall, so not only warmer in winter, but cooler in summer. Be warned though, it's not cheap, with a 2400x1200x25 sheet coming in at about £20. You'll also need to put a layer of plasterboard as a finish, though 9mm should suffice.

Worth the effort though.

Cheers Clive

=>Basically, what you want to do is insulate the underside of the =>actual tiles or slates, and that can be done by plating the underside =>of the rafters with plasterboard or insulation board.

Necessary but insufficient. Even in the (relatively} mild climate of the UK, plastic foam sheet or fiberglass batts should be used. Also, a vapour barrier (plastic or aluminised mylar film) between the wall covering and the insulation is an absolute must., _especially_ in a climate that tends to be some what, er, moist.

=>have to ensure that you provide for a fair amount of ventilation =>between the plating and the tiles/slates to prevent the possibility of =>dry rot. So it is worth involving a good builder to make sure that =>the insulation is done properly.

Agreed. Ventilation is promoted by the use of vents near the roof ridge, and by perforated soffits at the eaves. Again, an absolute must IMO.

IOW, find out what the builder offers in an insuklation package; The above is the elast you should expect. BTW, heating costs (and cooling, if you indulge in air-conditioning) are can be reduced susbtantially with careful insulation. One of the things I've nnoticed in my visits to my European relatives is that most houses are poorly insulated. Recent construction tends to be done better.

HTH

Wolf Kirchmeir ................................. If you didn't want to go to Chicago, why did you get on this train? (Garrison Keillor)

Wolf,

I did use the word 'basically' :-)

Plating with plasterboard on the underside of the rafters (plus a moisture barrier as well) will provide reaonable heat insulation and it's easy to leave pretty good ventilation space for the roof. I've used the same system in my single brick walled garage and I can keep that area comfortably heated in winter with a 1.5kW convector heater. However, as soon as you start talking about stuffing whatever material into the space between the rafters, then you can run into a lot of ventilation problems if you don't get the advice of an expert.

Jim.

I used 50mm Celotex which I got for about 18.50 a sheet (2400x1200) about 15 months ago. Took a little shopping around, but not much, got it delivered from a builders yard 5 miles up the road. There was probably VAT to pay as well. Jewson's wanted about £25 for same, so it is worth making the effort.

I just used mine between the rafters. That means cutting to size which is time consuming, but I couldn't afford to lose 2" off each side of the interior space. You have to get an air-tight fit or it's wasted effort; my builder gave me a tip which is to press it up hard on one edge and then give it a wack on the other edge which will form an indent to guide the marking out. Then it just takes a few wacks to get it in place. Don't rely on measuring, especially so if you're going to have to cut it downstairs into pieces narrow enough to fit through the loft hatch. You can be sure the rafters aren't parallel or evenly spaced. In my 70 year old roof some weren't even straight. By the cheapest panel saw you can find to cut it with and beware of the fine dust created (ie use a mask and clear up properly afterwards).

My rafters are 4" deep and building regs require 50mm air gap beneath the felt, hence the choice of 50mm insulation. You can use galvanized nails 2" in to make a stop for the insulation. If I'd had more room I could have fitted 75mm Celotex, say, and had it standing proud of the rafters by 25mm. In that situation you just nail 25mm battens to the rafters to give you something to attach your plasterboard onto.

Have a look at the Celotex website for technical data. About from very good thermal properties you will also discover it is fire retardant so that is one less thing to worry about.

One final thing - the offcuts are great for scenery. As light and easy to work as expanded polystyrene but not the same fire hazard.

HTH Regards,

Simon.

Thanks for the info chaps. I checked out the Celotex option, and based on a few rough measurements, it'll cost £544+delivery+VAT just for the Celotex...Ouch!!!

The building regs are more complex than that. If you line the inside of the rafters with insulation then you also require ridge vents equivalent to a continuous 5mm opening and eaves vents equivalent to a continuous 25mm opening as well as the 50mm air gap.

You will not be able to sell the house without lying to prospective purchasers and their solicitors.

Andrew

Surely that's the real estate agent's job, isn't it?

Surely that's the estate agent's job, isn't it?

I started thinking about the loft; and then looked into the building regs. issues. My conclusions were as follows (based on a fairly modern house) :-

1. It would cost several thousand pounds to provide a 'room' in the loft that would actually meet building regs; and hence not make the house virtually unsellable.
2. It would still be freezing cold in winter and boiling hot in summer.

1. Where would I put all the crap / family heirlooms that are currently in the loft?

In the end I decided to leave the cars outside & use the garage ;-). Other option considered was a good quality shed : a lot cheaper than doing out the loft properly; if you have enough garden to put it in.

I would hope the purchasers surveyor would spot the problem, but in the UK (I assume from your domain that you are not), the vendor usually (always in my experience) has to fill in and sign a form to state what is and isn't included in the sale, details of disputes with neighbours, etc., and, crucially in this case, details of any alterations to the property that may require planning consent or building regulations approval. If the latter are not in order then alarm bells should start ringing. As a purchaser I would walk away or negotiate a discount to cover the costs of putting matters right, which would be substantial if the roof timbers are damp due to a poorly thought-out conversion.

Andrew

...

Do you mean just leave a gap at the top and bottom of the insulation? If so that doesn't sound particularly challenging.

I believe what's meant is vents to allow outside air to flow in through the soffit (eaves) and out through the ridge. Such vents are standard in Canadian construction; however, loft rooms are uncommon and insulation is usually blown in between the ceiling joists. Houses in most parts of Canada have basements because of the need to pour foundations below the frost line (4 to 6 feet).

Martin S wrote: -

Also Martin, given the way Canadian roof trusses are built, using 2 x 4s, there's no room in most attics for a room as the extra trussing (Required by using 2 x 4s) in the way.

-- Cheers Roger T.

of the Great Eastern Railway

Well, yes, the whole roof and attic space is built on the assumption that it will not contain habitable space.

I found that the exterior walls of my house (built 1997) are 2 x 6 studs on 24" centres with R20 insulation, and 5/8" interior drywall applied over horizontal metal furring. With a high efficiency furnace (plastic DWV pipe for exhaust), we don't burn much gas.

Correct.

If you go to all that trouble and install power and lighting (and maybe heating) then the building control officer will probably say you have created a habitable space and then there's a whole raft of other regulations such as uprating the ceiling joists, means of escape, fitting a permanent staircase, fire doors on all other rooms off the stairwell, etc... You may also require planning permission if you have already used up some of you permitted development rights.

That's how most UK houses have been built for the last 20 or 30 years. Hence the high cost of converting the loft in a modern house, apart from the requirements listed above.

Andrew

We recently discovered a huge problem in our roof. The house was bought back in 1985, and came with a 20 year guarantee against parasitic infestation and wet or dry rot in the roofing timbers. 18 years after moving in, the first tentative steps make real use of the loft space discovered that basically a large number of the timbers have suffered about an inch of depletion on all sides thanks to woodworm.

Thankfully, this is a rather ancient and over engineered property - the rafters alone being a meaty 6"x3", and the support timbers being 18" squares, so when funds permit (the company who guaranteed the house woodworm free long since ceased to exist) it'll just be a case of getting in some people to stink out the loft with lots of lovely poisonous wood sprays!

Ronnie

--

Due to recent viruspams, any email containing the word "Microsoft" will not be received.

Andrew, I'm in Australia, and the onus here is very much on the prospective buyer to determine what, if any, problems of this nature may exist. In New South Wales, at least, there is nothing like the form you mention - which sounds to me like a great idea!

All the best,

Mark.