Insulation for a Swithland slate roof & gutter choices

[JoceAndChris]

Hello all and a very happy new year to friends old and new. I hope you're all doing well and sitting in gloriously warm, finished houses! :lol:

So we're having the roof completely reroofed this spring. In the 80s the previous owner stripped off the existing Swithland slate, which is original, laid on new felt, and put the slates back in their diminishing courses, ignoring the fact there's a shortfall of around 30-40% in slates. And he didn't insulate and we've all frozen ever since!

We're keeping all the original slates and buying extra. The quotes, so far, have ranged from 30k to 60k including VAT. The range is unbelievable!! It's around 145 sq m and all roofers seem to think it will take 4-6 weeks as each slate needs possibly damaged edges chopping off and moving up to a smaller higher position.

For guttering the latest one is suggesting removing the lead, lining the chestnut gutters with thin rubber, and putting the lead on top, as he says lead joins every 2 metres is just insanity in this day in age. The joins split and leaks occur. This sounds quite a reasonable decision to me, any thoughts?

Then the insulation. The more expertful roofers I've chatted with seem clear that exterior insulation which lies under felt and slate will alter the roof line and ruin the proportions and is in fact unfeasible. They all seem to agree we need a lot down on the attic floor. But, there's an attic bedroom in the roof which is currently very very cold. The ceiling is modern plasterboard above the rafters. On top of the plasterboard is felt and slate with no insulation. I had hoped to keep the ceiling as is but lay insulation on top of it under the felt. However I've just been told I can't as this will affect the entire roof line. So, to insulate this bedroom the latest roofer thinks I'll need to insulate the interior which will mean covering up the beams. Any thoughts on that would be much appreciated. I suppose sacrificing the look of beams may be worth it if the room becomes warmer.

 

[JoceAndChris]

 

[JoceAndChris]

this one shows the attic bedroom in the roof

 

[88v8]

Hello from someone who's house is neither finished nor particularly warm.

I would not dream of covering those beams. The modern obsession with insulation does so much damage to the look of period interiors.
To anyone who complained that it's cold, I would say that cold is part of the 'period' experience. Wear a jumper.

However, one could insulate to the thickness of the rafters, but not beyond, without spoiling the appearance.
Someone more versed in insulation materials will suggest what might be used and plastered on.

I suppose the variation in quotes is not untypical of builders. Partly depends whether they really want the job, how busy they are, how competent they are. I presume you'll go and look at a number of their previous jobs and talk to the owners.
You might send Doug a PM about the lead, he doesn't seem to be here so often nowadays.

Ivor

 

[plasticpigeon]

What about a "space blanket" type layered insulation between rafters and felt. It is expensive, but thin and has excellent insulating properties for its thickness.

 

[JoceAndChris]

What about a "space blanket" type layered insulation between rafters and felt. It is expensive, but thin and has excellent insulating properties for its thickness.

I'll ask him - thanks.


Agree insulation can ruin the look of things. However 4 grand a year on heating to have a not very warm house also has to be taken seriously. There has to be some sort of compromise! I'm quite used to the cold, guests, however, complain, especially the children. That room is around 9 degrees on a chilly night.

 

[JoceAndChris]

Oh, and in answer to Ivor's post about the importance of checking work and talking to satisfied customers, yes I think that's crucial! I'm mainly interesting in people with proven experience of roofing G1 buildings and preferably National Trust or English Heritage buildings in Swithland, which as you might imagine narrows it down to a very few individuals as Swithland isn't mined anymore and is becoming increasingly rare. However I've been lucky in finding the roofer who did Stoneywell. Not had his quote yet though.

 

[malcolm]

I have just finished insulating my loft and attic to current regs and am very pleased by the result. It is warmer upstairs and heating bills have more than halved (though I predict around a 30-35% reduction in bills - much of the reduction will be due to the unusually warm weather so far this winter).

Have a read of the English Heritage guide to insulation at rafter level https://content.historicengland.org.uk/images-books/publications/eehb-insulating-pitched-roofs-rafter-level-warm-roofs/heag070-insulating-pitched-roof-rafter-warm-roofs.pdf/ I've not read it but their advice is generally sound.

Consider damp when you consider insulation and roofing. I decided the best roofing system for me was a breathable membrane above the rafters with an air gap of at least 50mm between the membrane and ceiling or insulation and eaves vents supplying a good draft through that air gap to keep the structure nice and dry. My rafters were 4 inches deep, proper sturdy Edwardian ones and I had only a small area of sloping attic roof. If yours are Georgian they might be a bit thinner.

I guess the choice is between adding a layer of insulation above the rafters and adding insulation between the rafters (or both). The thickness of rafters could be increased by screwing some wood to them. The only issues in increasing the thickness of the roof will be gutter detailing, leading detailing, and the dormer window. Roofers probably won't like the thought involved and will say it is impossible.

It is possible to plaster onto wood fibre board insulation which could be a possibility for between rafter insulation if you want to leave some of the rafter exposed.

 

[JoceAndChris]

Interesting post - many thanks. Will have a good read of the EH guide.

Fab that you have reduced bills, we really hope for that too!

 

[Flyfisher]

What about a "space blanket" type layered insulation between rafters and felt. It is expensive, but thin and has excellent insulating properties for its thickness.

That's what we opted for. Like Joce, we have attic rooms and really needed a 'warm roof' if there was any chance of getting some practical use out of them without spending a small fortune on heating. Raising the roofline is always a concern, but I think much depends on the existing roof details and things such as dormers, gables and guttering.

I recall a lot of discussion here some years ago about the effectiveness of 'multi-foil' insulation, with some people and sources being quite 'anti' in terms of not believing it could perform as well as the manufacturer claims. In practice, I was less concerned about the absolute performance because anything would have been a major improvement to our failing reed + plaster 'sarking' and pantiles and it seemed the only possibility for a warm roof without major (and unreliable?) works between the roof timbers while minimising the overall height increase to the roof. I also didn't have to meet any specific thermal performance requirements as there was no building control involvement. It also helped that our three dormers were very rotten and had to be rebuilt anyway, so a bit of extra roof height was very easy to accommodate.

After much discussion with our CO we settled on a design that limited the height increase to about 60mm and kept all the existing roof timbers untouched and fully visible from within the attic rooms. Basically, we stripped the roof, covered it with plywood (which added significant structural stiffening), covered that with counter-battened multi-foil insulation, covered that with breathable membrane, then battened and pantiled. Five years on it all seems fine (early days, I know!) and the attic rooms are warm (ish) just from the residual heating from the rooms below (no insulation on the lower bedroom ceilings (yet!).

Given the gutter detailing at BC, I would guess that a 60-ish mm roof height increase would be fairly easy to accommodate and the end result would be indistinguishable from the 'before'. Anyway, just some thoughts and experiences.

 

[jocelyn plummer]

Definitely keep the timbers exposed--

 

[mims&pip]

Mmm, I'd definitely want to keep the timbers exposed too Our last house had two second floor attic bedrooms with a multitude of attractive exposed timbers. As our roof was (newly) thatched, we found that cold wasn't too much of an issue in those rooms (although I'm another one who throws on another sweater if I get chilly!) but if we had I think we would have investigated the space blanket idea.

Mims x

 

[Feltwell]

Joce, for the lead guttering, I think building paper underneath would be the way to go rather than rubber - make sure the lead can move freely and doesn't stick. BUT..... you really need the services and knowledge of someone who knows what they're doing with lead, which is not me or a general roofer who does a bit of leadwork!

I'm sure Doug (DJH) on here can help with some advice as it's very much his area of knowledge.

He's a bit of a way from you, being Birmingham based, but I thoroughly recommend Quinn Bytheway as a lead contractor. See link below.

http://periodproperty.co.uk/forum/viewtopic.php?f=1&t=12804&hilit=lead

Done properly in lead - and there a lot of people who *think* they know how to work lead - that guttering should outlast you & I ! Joints are fine and necessary if properly detailed. If not done right the expansion and contraction will eventually fracture the lead somewhere.

 

[plasticpigeon]

Ah, so that's who you used. I wanted to use him too, but he gave me a crazy quote so I used someone else. Then he got back to me and said he had sent me a quote for a different cutomers job which is why it seemed completely different from what was discussed. Shame but it looks like he did a grand job on your porch. I shall use him if I ever need any more work doing.

 

[Flyfisher]

Done properly in lead - and there a lot of people who *think* they know how to work lead - that guttering should outlast you & I ! Joints are fine and necessary if properly detailed. If not done right the expansion and contraction will eventually fracture the lead somewhere.

I understand the contraction/expansion issue with lead, which is why I can't understand how lead guttering can survive over a long period of time. Overlapping 'joints' on a slope is one thing but gutters have to be watertight and therefore (I assume) require solid joints, which must surely compromise movement and therefore cause splitting and cracking with the inevitable expansion and contraction.

Too little knowledge, I suspect, but perhaps DJH knows the secret? Unless he's been sworn to secret and only a funny handshake can open his lips :wink:

 

[Feltwell]

My (very!) limited knowledge of lead does tell me that if you use heavier gauge lead then the joints can be further apart. As for the joints, I think they may have to be coincided with an internal step in the gutter, but Doug may come along and tell me I'm talking cobblers!

A little knowledge can be a dangerous thing, but I do know now that with lead it's the detail of how it's used and (in particular) jointed that is the key to it's lifespan. Badly detailed lead can fail quite quickly.

God is indeed in the detail!

 

[JoceAndChris]

Thanks for the posts chaps! I wonder what Doug would think - I'll pm him.
I've had 6 roofers round now and they all agree lead gutters are an improbable nightmare. The previous owner gave his his welding kit and said we'd need to learn how to use it. The very expertful roofer who did Stoneywell said my lead joints would need work every 3 or 4 years, unless I used the lead expansion joints. The trouble is they have plastic ends and so would give the lead gutter a stripey sort of look, as the cottage is one and a half storey height the edge of the guttering is very visible and especially from certain raised points of the surrounding land - like the back garden.
I'll check out building paper - thanks Feltwell.
If it were a piece of really pretty decorative lead work I'd want a skilled artisan but it is a functioning plain old gutter and everyone seems agreed that chestnut lined in lead is a pretty but stupid idea!! After all look what happened to the original guttering which was oak! The lead leaked and the gutter rotted out hence being re done to the original pattern, but in chestnut, in the 80s, at the vast cost ( for then) of £8000!!!! Now it's rotting again! We have to find a better system.

As for the thin foil space blanket insulation, I'm worried that it isn't breathable, so you'd no longer have a breathable roof structure. Isn't that a major potential problem?

Also I don't know why they're all saying a 60 mm increase in roof height isn't feasible because of details and proportions, but that's what they're all saying. And also I'm going to need the bows and wonks to be recreated which I'd guess would make any rigid insulation pretty impossible to install.

 

[Gareth Hughes]

I can't work out how Flyfisher's use of space blanket amounted to a 60mm increase in the roof height? even with plywood sarking and counterbattens that seems a lot.

 

[plasticpigeon]

Space blanket certainly isn't rigid, it is many layers of foil with very thin layers of some kind of insulating material between. I'm not sure whether the non "breathable" nature of it is a problem. It is my hunch that if you followed something like what flyfisher has done then there would be air flow between slates and laths like in a normal roof, and the breathable felt would allow air flow to the counter battens, so the only area that might be awkward is between space blanket and plywood. I'd imagine there would be venitation at the eaves allowing some air flow between ply and rafters, and I'm sure your ceiling is lime, so I'm sure it would be workable.

 

[malcolm]

From my own experience of tradesmen things are described as impossible if the tradesman has no experience of doing it. Roof insulation is far from impossible. Figuring out how to do it yourself is probably essential - you might be able to persuade cheaper tradesmen to do the work if you can tell them how to do it, and you could monitor the work of those who claim to know how to do it. My roofers were disappointing.

Can't help with lead gutters. You do need a break every now and then to allow for expansion and contraction in a flat run to avoid cracking. The length of run depends on the thickness of lead. If you have the fall I wonder weather an occasional bend in the lead would allow for expansion without risking cracking. Something like a 1m run, 45 degrees bend for 10mm, 1m run etc. Doug would be the one to throw that out of the water.

I have used non breathable insulation only where there is good ventilation on the cold side. Can't see how it wouldn't cause moisture problems otherwise.