I’m trying to insulate my roof space while it’s still warm up here, abd while 70% of the roof structure is open and accessible, part of the roof is not. The upper rooms are partially chamfered along the exterior walls by the roof. This means that, from the loft, you can see the top of the exterior walls about 2m down a 100mmx400mm cavity that follows the roof angle. I’m trying to get some insulation down those gaps because when it’s -20 outside like last year the chamfered ceilings literally have cold air rolling off them and there radiators/boiler struggle to keep up. I could of course install bigger rads (I think we’re fairly low on radiators WRT boiler output) but I’d much prefer just not to lose the heat so I started slipping space blanket down the gaps. Problem is the gaps are riddled with nails and it’s REALLY difficult to get the insulation down there – took 2 of us about 3 hours to get 4 gaps done, there’s about 20 more to go and the last one won. We were using two super-long pizza shovels made from ply and 1×1/2 to trap the insualtion and shove it down, but thats practically impossible when the nails get in the way.

Our two remaining options are blown insulation (££) and pulling the glass from the space blanket and stuffing it down manually with a long rod 😡 .

Any other thoughts?

Insulate inside the room.

It’s possibly/probably not a good idea to stop the airflow inside your roof up from the eaves.

I’d considered the airflow issue (and initially thought about sheets of polystyrene until I saw the price as I thought it’d allow it to flow still) but then I realised two things – 1) all of our soffits are completely sealed and rendered over by design, no airflow seems to come from down there other than from the cavity vents at the base of the house and they’re mostly blocked and 2) It’d be impossible to insulate the inside of the rooms without completely re-decorating a newly decorated house and shrinking the room size with lower performance?

There is a programme called “Holmes on homes” which is Canadian based.

They frequently use a spray-on expanding foam (bright blue stuff) for the underside of roofs etc. Obviously it does need enough access for the lance but nails are not a problem.

Given Canadian winter temps it must be very effective.

Now the catch. I have not a clue if it’s available here or meets UK building regs.

Just the slopey bits.

Sticking insulation down those holes may cause the inside face of your roof to get colder, and especially with no air flow could lead to condensation problems,

Hmmm available is the issue, building regs not really the concern assuming it’s not flammable – anything is better than nothing in this case. I’ll see if I can track down what you mean. I’ve spotted Icynene while searching the local area for blown insulation but it looks quite expensive by the justification that it’s used in top end older homes (Barn conversions etc) and in the long term it pays itself back etc. Cheers for the tip, I’ll see if I can see something similar here!

They frequently use a spray-on expanding foam (bright blue stuff) for the underside of roofs etc. Obviously it does need enough access for the lance but nails are not a problem.

Uh oh.

Uh oh.

Elaborate?

Just the slopey bits.

Sticking insulation down those holes may cause the inside face of your roof to get colder, and especially with no air flow could lead to condensation problems,

Couldn’t really just insulate the slopey bits I don’t think, as I say it’d be a re-decoration of the whole upper floor – hundreds of quids and weeks of effort.

Insulating there will of course cause the inside face to get a bit cooler, but to be honest it can’t be /that/ much colder than it is now when it’s properly cold outside. I never have any issues with condensation now even on the uninsulated bits of roof or the single-glazed roof window that’s up there, so I can’t see there being further problems. One worry was that I’d not be able to see leaks until they were fairly significant but there’s only so much I can do to help that. I’ve no way of quantifying the risk though. The roof surface is fully sarking’d (15mm thick) with felt on that and tiles on the outside.

insulate inside the room, and leave circulation gap there.

And please dont spray on foam…please.

We used blown sheeps wool to get into our out of the way bits, has the benefit of being natural, non toxic and fireproof. As well as cheap.

I wonder if sheeps wool is available in the UK (as insulation, I’m not thinking polyester sheep here!). The thing I like about the f/glass wool is that it still breathes, even in the space blankets – they’re open at both ends and they don’t TOTALLY fill the void side to side.

Sheeps wool is available – v expensive if that is an issue. Blown needs something to contain it – but you are trying to insulate a slope aren’t you? You do need an air gap beneath the roof.

Try an on line calculator to check you have properly sized radiators too:

http://www.radcalcs.com/

Dont block the flow of air. And the cavity vents down at ground level won’t be venting anything other than the u/s of your precast floor! They will periscope downwards. How old is the house? Best thing to insulate eaves that are in rooms is cellotex cut between rafters but this is obviously done during construction. Also why is the “space” riddled with nails? That suggests to me whatever they’ve intended to nail into has been missed!!!

Again, you need the airflow in the eaves, there should be a gap under the tiles to allow plenty of airflow. Any insulation will give instructions to not insulate right into the eaves (as well as not insulate under the cold water tank)

The spray on foam is available here but a lot of people don’t like it…it sticks to everything and if the roof ever need repairs it is a nightmare. And I’v never seen it as a DIY solution.

Having seen how easy it is for a professional plasterer I would pull the sloping ceilings down, fit slabs of Kingspan in between the joists then re-board and re-skim. However that’s a dusty and expensive option although if you wanted to you could pull down the entire ceiling and take the opportunity to wire and fit nice bright halogen or LED downlighters….

To do it DIY, could you just slide slabs of Kingspan down into the voids?

Pull the plaster down, then use thinsulex tlx silver multi foil insulation. Gives great insulation in tight spots.

agree with what global & sam said for best effect,

Have you tried making temporary ply liners for the voids that you can slide in like a pocket into which you can push some glass batts that you have cut to fit, then extract the ply liners.

led downlighters? have you calculated how many you would need and the cost of replacements? working in a house last week with 72 led downlighters that were a fiver each to replace, the guy ( an electrician) was removing on a cost basis. rad calcs rarer end oup giving you bigger rads.. infact 90% of the calcs we do for customers show that existing rads are too big! i’d suggest replaceing with modern ( even cheap) new rads of a similar size which will provide more heat without costing more ( todays job infact, replace 8 10yr old single panel rads with similar sized new cheap rads) let your rads work properly allow them to radiate and convect heat ( dont put stuff infront or above them) eliminate draughts.. thats how houses get cold.. doors windows fireplaces

Putting downlighters in the ceiling below a roof also generally V bad as it means cutting through whatever insulation you’ve got there.

I tried temporary ply liners to insert the insulation but the space has a small opening and as I say, it’s riddled with nails (from the roof tiles) so while it worked on a few, on others it just made it impossible to get the stuff down. Kingspan type stuff is possible but it’d have so many gaps around it it’d bearly serve to insulate anything. The whole point of the insulation is to stop the air circulation convecting heat away from the ceiling and the kingspan would struggle to seal against edges and tops/bottoms due to the uneven structure, so it’d probably be just as bad as now but more expensive.

The wall vents are both at ground level and directly into the brickwork at 2-3ft up, they’re not just there for the floor space I’m fairly sure. They’re also throughout the inside of the house but most have been sealed up prior to my arrival. house is a 60’s ish brick and block construction. There’s never a hint of damp in the loft (unlike my old place which would literally drip with condensation when it was cold out).

As far as I can see the shear quantity of ventillation and these inaccessible spots with no insulation are the entire reason the house is cold.

http://www.ebay.co.uk/itm/80-CF-POLYSTYRENE-BEAN-BAG-FILLING-BEADS-REFILL-BAG-/280726045754?pt=UK_Home_Garden_LivingRoom_BeanBags_SR&hash=item415c93843a#ht_1283wt_905

As far as I can see the shear quantity of ventillation and these inaccessible spots with no insulation are the entire reason the house is cold.

And not damp.

They frequently use a spray-on expanding foam (bright blue stuff) for the underside of roofs etc. Obviously it does need enough access for the lance but nails are not a problem.

Given Canadian winter temps it must be very effective.

Now the catch. I have not a clue if it’s available here or meets UK building regs.
Not sure what the legal point is, but I know our neighbour has that stuff on his roof and can’t sell the house – every time he accepts an offer, the buyer’s report throws it up and the sale falls through. He just rents the house out now.

And not damp.

Don’t think so, no. As I say, it’s bone dry up there. Remarkably so. There’s a very chilly stainless flue that goes up and out and that never gets even a hint of condensation even mid winter, and even when there was a leak from a missing tile.

(drawing to help the discussion BTW)

roof by j.buckle, on Flickr

I used Celotex in my old house – it’s thin enough that you still get an airflow behind but gives good insulation.

they do a 25mm foil version that’s quite good but the thicker stuff is probably better and you have room for it.

biggest advantage is that it’s stiff so you can shove it in gaps without it just folding up.

The problem I have with the sheet form stuff is if it goes in and sits at a jaunty angle/doesn’t sit flat against the bottom you’ve really not gained anything at all, and since it’s down a gap I can’t get a hand to I can’t make it do anything it doesn’t want once it’s gone down there?

make up an oval section of plywood with a broom handle on it at 90 degrees.

As you twist the broom handle the oval section pushes against the underside of the roof and also down onto the insualtion board pushign it into place. As it’s oval you can get it into place by pushing it in with the ‘narrow’ side between roof and insulation and it deals with a variation in gap as you twist it to brign the thicker part into play.

Edit: imagine this but with an oval piece of wood instead of the paddles.

Its a cold roof design. If you clog it with insulation, you will end up with damp. The best bet is a celotex / kingspan sheet, with a void for air flow above. If you can’t manage that, then insulation inside the room at the thermal bridge (sloping bit) is your best option.

Indeed an interesting option – I have been using a broom handle as it is but the space is so confined at the top it’s nuts and the nails don’t help getting things down there. I’ll think on it and see if I can find a source of cheap solid panels.

working in a house last week with 72 led downlighters that were a fiver each to replace, the guy ( an electrician) was removing on a cost basis

Interesting. What was he replacing them with?

There’s a company called Black Mountain that sells wool based insulation