Insulating a roof

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Insulating a roof

Post by oldpeculiar » Tue 18th Aug, 2020 11:38 am

Hi All
I live in a late 1700's weavers cottage, The top floor (used to be the working area) currently serves as a bedroom/playroom. Trouble is it's not at all insulated - a layer of plasterboard, roof felt then the slates. It gets very cold in the winter (despite having 4 large radiators) and very hot on a warm summers day (infrequent as they are).
I'd like to get insulated, I've seen other houses in the areas with insulation/plasterboard fitted between the large beams, presumably fitted to the underside of the smaller timbers. I did wonder about insulating between those, although that would be very difficult to get acceptable snug
Obviously this will be subject to the usual building consents, but my biggest concern is how this can be done so as not to damage the timberwork, moisture being the main risk. Does anyone have any thoughts on what would be involved? Would we have to take the roof off and fit breathable felt? Would insulating between the beams be viable?
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Re: Insulating a roof

Post by Lime » Wed 19th Aug, 2020 6:07 pm

I think you've got your work cut out for you here, insulating under the ceiling will disfigure it, not be easy and probably be accompanied by condensation problems.
On top of that it may still be a difficult area to heat.
I'd consider taking the roof off and laying insulation on top of the ceiling but from your description the roof level would have to be raised to accommodate it.
It would be expensive and maybe impossible to do.
Not being funny but if the area is a bedroom'playroom have you considered putting up a large tent/marquee to play'sleep in?

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Re: Insulating a roof

Post by MatthewC » Thu 20th Aug, 2020 4:37 pm

oldpeculiar wrote:
Tue 18th Aug, 2020 11:38 am
I've seen other houses in the areas with insulation/plasterboard fitted between the large beams, presumably fitted to the underside of the smaller timbers.... my biggest concern is how this can be done so as not to damage the timberwork, moisture being the main risk.
You're right. I have seen houses insulated like that and in most cases I think they are storing up a damp problem for the future due to the lack of ventilation around those beams. I don't know the answer, which is why my house (with flat ceilings) has lots of sheepswool over the joists in the loft which is well ventilated - a "cold loft". However, it is warm!

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Re: Insulating a roof

Post by CliffordPope » Fri 21st Aug, 2020 4:53 pm

I think youv'e got a choice between appearance and comfort.
Personally I'd go for appearance any day. But then I grew up in a house where there were icicles on the inside of the windows and the bedrooms were totally unheated.
Children don't feel the cold!

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Re: Insulating a roof

Post by Greg.Hobson » Thu 27th Aug, 2020 9:26 pm

Hi there.

You don't say where you are, but from the style of house and language ("Weavers") I would guess W. Yorks or Peak District.

We are above Holmfirth with a south-facing house and had a similar problem, compounded by the failure of the felting from only c.25 years earlier above the windows that meant it was a whole roof job. I too wanted to reveal the rafters in our bedroom (they were previously hidden) and didn't mind how much actual depth to be on show but the rest of the roof (about 2/3) was lost in an attic so we didn't mind losing the rafters in there.

In the bedroom, I opted for keeping about a centimetre of the rafters on show, then plasterboard, multi-foil insulation (which then required about an inch air gap above and below) and we put 2 inches of modern foam above that, then the modern, breathable felt, battens and slates - which are stone in our case - which made up he required level of insulation (just). This left the bottom of the rafters on show and only added about 2" to the roof height over the bedroom. In the attic, we lost the rafters behind 2 inches of foam insulation with more foam insulation (3 inches if I remember rightly) between the rafters, then felt, battens and slates.

We were lucky in knowing a very good roofer and mason in the area. He lost the difference in height across the roof ridge caused by the differing insulation choices by careful selection of the stone slates, as they varied quite significantly in thickness. The final fractions of an inch were lost in the judicious use of fixative on the ridge tiles. This was about 7 or 8 years ago and cost £13k, which included the cost of 4 new oak purlins and various repairs above the windows that caused the initial requirement, but I put up the multi-foam myself as it was fairly new at the time and the roofer had not come across it before - he just rebuilt the whole structure and then worked on the top and I worked on the inside.

The effect has been quite marvellous. We too previously suffered from too cold in winter and unbearably hot in summer. Our bedroom is now the most evenly regulated room in the house regarding winter/summer extremes. We heat the house in winter with 2 wood burners in the dining and front rooms, at the bottom of the 3 stories. We keep our bedroom door open in winter as the hot air from downstairs gets up there and is not lost anywhere as quick as it used to be and we keep the bedroom door closed in summer to stop the same convection driven from the pleasntly-warm bedroom and the bedroom getting too warm and the said dining and front rooms getting too cold (in summer!). The wood-burners mean we rarely have condensation issues. The modern felting is wonderful stuff. I remember it raining heavily when we only had the felt up and I went up the scaffolding (in the bedroom) and stood with my face close to the felt. I could feel the dampness of the air, but wthere was no actual water ingress from the rain - I remember how amazing I thought it was.

We insulated the Gable end wall with 4 inches of sheeps wool insulation that we did ourselves and that was also a game-changer. In winter, the cold used to "fall" off that wall onto our shoulders when we sat in bed prior to the work, but it is now our go-to room, particularly over summer, with the requirement to keep the wood burners fed over winter meaning we get plenty of exercise up and down the 2 flights of stairs.

Sorry for the long post, but I believe you can get a solution, but it may require a lot of research and effort and an excellent and willing roofer!

p.s. Sorry, I forgot to mention that the multi-foil I used (I forget the name) was made specially to fit between rafters. It is effectively wide strips with "wings" down the edges. The "wings" are essentially just the foil parts extended to provide a flat, flexible fixing surface that can be run up the sides then over the top of the rafters so you can achieve the degree of tension required for it to perform at its best. I fitted it myself, so it can't have been all that difficult, but I remember having to be reasonably precise to get it just right. The roofer then put 3x2 on top of the rafters (complete with the multi-foil) to give space for the extra foam insulation on top and provide the top air gap.
Last edited by Greg.Hobson on Fri 28th Aug, 2020 11:12 am, edited 1 time in total.

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Re: Insulating a roof

Post by Flyfisher » Thu 27th Aug, 2020 11:14 pm

I faced a similar dilemma with our C16 G2* timber frame house with three large attic rooms. In one respect I was fortunate in that the roof was in a very poor state and had no membrane so I was effectively forced to strip the roof anyway. To make the attic rooms more habitable I wanted to create a 'warm roof' but I also didn't want to cover any of the attic timbers. Because of the gable parapet wall I had some scope to raise the roofline but obviously wanted to minimise and increase.

In consultation with our CO (obviously!) we settled on boarding over the entire roof with 9mm marine ply, then covering the ply with 30mm of Tri-iso Super 10 multifoil insulation held down with 25x50mm counter-battens. A breathable membrane was then fixed over the counter-battens and new tile battens fixed to the counter-battens and the original pantiles replaced on top. The total roof lift was about 60mm, which was easily lost in the gable wall detailing so that the finished result is indistinguishable from the original . . . well, from the outside anyway. From the inside it's no longer to see the sky through gaps in the pantiles :wink:

Multifoil insulation could be considered a controversial choice depending on who you talk to, mainly because some people are sceptical about its quoted insulation performance figures. However, I was not aiming to meet any building regulation requirements, only to massively improve the habitability of the attic rooms in question. In that respect it has certainly been successful.
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