Loft Insulation - Best Type and Tips for Installation

[L Reid]

Hi guys,

More drama from the new property...

I need to insulate my loft. As we don't have a loft hatch, father-in-law and I proceeded to cut one yesterday (in to a ceiling lined with 2 inches of pitch, that was very messy... and I thought sanding floors was bad!). As the ceiling was plasterboard (suspended below the old plaster lathes), the ceiling's obviously been replaced at some point so I have no idea why it didn't already have one.

Anyway, the house is about 120 years old, with a slate roof. There is no underfelt under any of the slates, just the slanted timber. The house is an Edinburgh colony type, so has the bedrooms partially in the loft space (i.e. there's areas of sloping roof above bedrooms without a lot of clearance I need to get insulation down into). I don't want to lift the pitch that's already there, as this would probably be incredibly messy.

As the loft is currently uninsulated (bar the pitch, which I believe is actually quite good as an insulator?) I'm after suggestions on how thick an insulation I should get, and what kind would be best. I had a scan through previous threads, and believe I also need to put down some damp-proofing? I'm also after suggestions on how to get the insulation down the 'loping bits'. Current plan is to slide a plank or two down over the pitch then slide the insulation down over it, then remove the planks, though there may be a better way to do it.

I currently have no access to the eaves at the moment, so may be unable to add insulation there. I'm not too worried about the eaves at the moment though as the downstairs rooms are fairly warm, it's just the bedrooms that are cold.

Any tips / suggestions? Any advice on insulating the loft hatch would also be appreciated as it's in a bedroom.

Thanks,

Leigh

[PoP]

Might it be worth contacting your local council? I was under the impression that grants might be available for insulating work involving older properties.

Perhaps someone else can advise?

PoP

[Toby]

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[L Reid]

Thanks for any/all replies.

One thing I forgot to mention is that with it being an older property the joists don't look very thick (6" or so?), so rockwool or similar might not be the best solution because of it's thickness. Are there higher insulation (lower U factor?) materials available?

Leigh

[The Natural Philosopher]

Best material goven type of construction is 50mm or thicker celotex/kingspan Isocyanurate board.

Cut to fit available space and tape well to prevent draughts.

Where you have a flat surface more than 4" deep, rockwoool is a cheaper alternative.

Both are unpleasant to work with - wear gloves masks and a boiler suit if possible.

[L Reid]

damp-proofing?

I thought the 'boardy' stuff was a bit more pleasant to work with than the rockwool? Should I worry about condensation, or should I be OK with a slate roof with no underfelt? It certainly let water in easily enough last week when a slate had moved.

Thanks again (again?!)

Leigh

[Andy Hall]

I found Celotex much more pleasant to work with than rockwool or glass fibre. Certainly I didn't find gloves necessary, but for cutting, especially with a power tool like a circular saw, a dust mask is essential and it's preferable to work outside. It does create a lot of fine dust, but only when actually cutting. I used an old table saw with an old blade and hooked up the dust extraction to the Bosch wet/dry cleaner. That sucks up most of the dust, but I still think that a dust mask makes sense. The most efficient way is to cut some or all of the pieces then get into the loft and have someone pass them up to you. The job goes pretty quickly then. Celotex has foil vapour barrier on both sides.

.andy

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[The Natural Philosopher]

Not much :-(

Hmm. Not really sure about rain ingress. Celotex is double foil backed - you wedge it between the rafters and then use special foil tape to get it sealed to the rafters - that puts a vapour barrier on the hot side, and you leave a gap to the slates for air circulation over teh rafter tops.

Pay a lot of attention to absolute draughtproofing. It makes a HUGE difference on a cold windy day. I may yet hit my loft with poly foam and silicone gun to get the last few out...

Underfeltinmg (sarking?) is very useful to cut down the wind level. I'd definitely say that if budget allows, a roof off, felt and relay is indicated.

Once the insulation is up, dry lining makes a decent finish.

You should leave the eaves open to allow air to circulate above the insulation.

[L Reid]

Thanks Andy. Did you replace existing insulation with it, and if so, how did it perform thermally compared to the 'old stuff'? Think I'll make a point of cutting it up outside, weather allowing. Did you just lay it flat, or did you use tape to hold it in place?

Cheers!

Leigh

[L Reid]

Thanks for that. I think I'll be going down the route of putting the insulation on the loft floor, rather than attaching it to the rafters, and was wondering if I'd still have to deal with the possibility of condensation if doing this. The roof is also partially within the bedrooms so I do have an angled loft-space to take care off. Pic here of a similar building :

[The Natural Philosopher]

I'll reply as well.

I used it on a new build in sections of sloping roof where the rooms were 'under the eaves'.

It is better than rockowool per unit thickness - about twice as good, but worse per unit £ as its about three times the cost!!

We cut the boards to fit between the rafters, friction fitted, and foil taped to the rafters, and taped over any smaller gaps - sometimes using scrap bits to in fill the odder parts.

We didn't use it on any flat surfaces - that was all rockwool, since we had adequate depth there.

Interior was clad in plasterboard laid flush to it.

Main problems have been with draughts. You MUST make sure there are no channels up which icy winds can flow to cool the plasterboard. With hindsight, I'd have gone round with a gun of expanding foam to lock it all in place and seal the gaps rather than rely solely on the tape. This problem was exacerbated by the Building inspectors insistence on huge ventilation holes in the soffits and roof ridges, that deliver a massive draught over the top of the boards as laid.

I mean I agree with venitlating the timbers, but not turning the loft into a wind tunnel...:-)

[Andy Hall]

Leigh

I had rather different projects to you which was to insulate the roof and walls of a garage with a pitched roof and the same for a cabin.

I looked at your original post and can't quite visualise what you have and were the insulation would go.

Also, it is important to be careful that there is appropriate ventilation of the timbers with whatever you do. You don't want to endup with a situation where timber is boxed in with insulation and a vapour barrier without being ventilated.

I suppose the closest situation I had to yours was the garage roof, so I'll describe what I did there. This roof is pitched, has conventional roof trusses, felt and then battens and tiles. For the environment, which is a workshop/garage I wanted to have reasonably good insulation to allow that the space could be heated to a comfortable temperature (16-18) for working at reasonable cost. I did the calculations and 50mm Celotex would give respectable results for what I wanted. If you want to do something to achieve Building Regulations levels for a new property, it needs to be rather thicker. Details are on Celotex web site and the requirement for Scotland is tighter than for the area occupied by the heathens to th south.

The Celotex web site shows a couple of options. One is to place some of the material between the rafters and some on top (i.e. furthest from the tiles) using two thinner sheets. The other is to put a single sheet over the rafters. This is what I did because I didn't mind losing 50mm of space. Where you use 70mm for example, then you may think it's too much lost and want to do the two sheet arrangement. There are dimension reasons as well. My rafters have a depth of about 75mm so I could have put 50mm material between them and still have had 25mm behind for ventilation. Had I wanted to use 70mm, it wouldn't have been enough.

Anyway, my method of fixing was to cut the pieces and attach them to the rafters using 70mm dry wall screws and 25mm penny washers with small holes so that the screw would not go through the foam board. I then taped over the joints to stop air flow from front to back. The space behind next to the felt is ventilated by having a soffit vent between each pair of rafters and making sure that the space behind he Celotex next to the felt is open to that.

I don't think that using tape as a fixing medium is that good unless you use thick duct tape - I could see the adhesive deteriorating in hot weather. If you are going between joists or in any case , the main purpose of tape is to seal and prevent air leakage through.

.andy

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[L Reid]

Magic, but hopefully you'll also see the other questions I asked under your branch too! I'll post 'em under Andy's thread to try and bring things together again.

Leigh

[L Reid]

Hopefully this will help:

one's were in are the flatted cottages rather than tenement block. Bizzarely our flat's actually in the last one (pic on RHS, 1st flat on left not in shadow), but taken a few tears ago. Interesting... the chimney looks as if it's leaning in that one too. I might also try and get some shots of the inside of the roof as that'd probably make things a lot clearer.

Cheers!

Leigh

[Andy Hall]

Nice places. What is the background to their being referred to as Colonies?

.andy

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[L Reid]

I'm actually not sure! I've managed to dig up quite a lot of history about these buildings, and it does make an interesting read, though no where does it state why they're called 'colonies'. I believe there's something similar in Dublin? The majority of the colony developments in edinburgh were done by the Edinburgh Co-operative Building Company, which was basically a conglomerate of lower middle tradesmen (stonemason's etc) that got together to build decent houses for themselves and their families, with their own gardens.

If I find some links I'll post 'em, as their history is interesting reading (but probably moreso if you're living in them!).

Leigh

[Rick Dipper]

You cut celotex with a table saw. WOW man you must love your power tools.

I cut it with a hand saw or a bread knife.

I gave all the spare bits to the kids to play with. They can cut it, and nail it (6 inch nails), and think they are doing real woodwork.

However back to the orignal question. If the loft ios flat and empty, then get one of these guys who can run a pipe upto the hatch and blow the stuff in.

Rockwall is allfull stuff. You should spend a fortune on protective gear. Wickes have it at good prices. B&Q = rip off. Celotex in a loft sounds cool, but its much more work to cut it all neatly, and a pain to get in if you loft is not flat.

Rick

[Andy Hall]

I did say an *old* one - which was also cheap and is used for rough work like this - with a old blade.

You can also do that, but it is not as neat with a bread knife, although the latter is useful for removing small pieces so that sheets can be fitted around timbers.

This is a bad idea. There is still some production of fine dust when the pieces are cut and there are strands of glass fibre in the hicker sheets such as 50mm for reinforcement.

upto the hatch and blow the stuff in.

Probably a bad idea because the stuff gets everywhere and produces dust.

I think you mean Rockwool....

B&Q = rip off.

a pain to get in if you loft is not flat.

Hence the use of a power tool. A circular saw with an old blade would be equally effective. Polyisocyanurate foam has approximately half of the U value (equals twice as effective) as other materials.

.andy

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[IMM]

A good idea as Warmcell will seal up the loft preventing air escapes and is the erqiv of insulation that is 25% thicker. Put 300mm at least in the loft. The extra cost of spraying in the extra is minimum.

Install lights in the loft and make sure the hatch is sealed as much as you can while spraying.

[Andy Hall]

.. and the ventilation to prevent timber decay comes from??

Why stop there? Fill the bedrooms and reception rooms at the same time.

Imagine my surprise when I couldn't get in through the front door :-)

.andy

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