Help with trying to insulate roof in an old house

canhefixit · 30-10-2013 03:45PM #1

I am starting to do up an old house and in the roof there is no felt at all behind the slates, now i havent the money to get slates lifted and felt fitted so was looking for another effective way to try insulate it a bit better.

I came across a product Therawrap and was wondering would this be a good method were I would staple it across the rafters covering the whole roof, so the attic then looks like its wrapped in tin foil.

Or even if anyone has any other ideas on the best way of insulating this type of roof any advise would be great.

Thanks

BryanF · 30-10-2013 05:14PM

show me its BBA / IAB Certification ? thanks (i dont believe one exists, their claims are hard to confirm)

your right to leave a substantial gap between slates and an insulation material.

is this speculative project or your family home? perhaps you could hold off until money allows for a proper job

canhefixit · 30-10-2013 05:46PM

BryanF wrote: »

show me its BBA / IAB Certification ? thanks (i dont believe one exists, their claims are hard to confirm)

your right to leave a substantial gap between slates and an insulation material.

is this speculative project or your family home? perhaps you could hold off until money allows for a proper job

It is now our family home and it the min I am putting in new windows, heating system, doors, kitchen etc and money is now getting tight..

Its an old cottage and is prop about 100 years old and the ceiling in the bedrooms are timber cladding kind of construction which I am getting replaced with insulated plasterboard and skimmed but before that I really want to do something effective with the roof but I defo wont have the money to pay roofers to take of slates and battens and re-felt with new battens and slates back down..

If the wrap stuff is the equivalent of sticking tin foil on the roof with very little effect i guess id just have to leave it but its really annoying me I have searched loads of insulation products and havent came across one to do this kind of job.

Jimmy Garlic · 30-10-2013 05:55PM

I think spray foam would be the way to go.

If you have an older property which has no felt under the roof, or your felt has perished or begun to, our spray foam insulation system can help. Provided that your roof is repaired by us prior to installation, spray foam will replace the need for a membrane and will also guarantee your roof, something which a membrane cannot. Foam insulation can also be used over old mortar underpointing, this will seal and guarantee the roof as well as stopping the old mortar falling into your loft. Spray foam insulation applied directly to the inside of your roof, to the relevant depth, will prevent any future leaks through the treated areas, it will also prevent condensation forming on the roof interior. Sprayed foam roof insulation will effectively seal your loft area creating a warm-roof when installed to the relevant depth, this prevents the build up of condensation even in the most severe winter weather and will protect timbers from moisture damage.

lets discuss the product type, please dont link to a specific product thanks

BryanF · 30-10-2013 06:06PM

canhefixit wrote: »

I have searched loads of insulation products and havent came across one to do this kind of job.

if your installing insulated slabs be careful where the due point will be and how the roof space is vented.will you be installing vent slates/vents at the eaves & ridge?drylinign under the rafters, wouldn't be my preferred option.

id say the same about the spray foam, whatever about a new house but one without felt - show me the IAB /BBA cert for its use

Ush1 · 30-10-2013 07:44PM

I would have thought some sort of felt would be essential.

I'm currently installing rigid ballytherm board insulation between our rafters and seems to be working well but in all installation literature it mentions roof felt.

Calibos · 31-10-2013 07:19PM

On a related note. We rent a business property that his gone down through the generations of landlords and us for the last 80 years. The feckers try to increase the rent every time 'We' try and improve the property. Felting and relaying roof tiles would definitely fit this definition soi we aren't prepared to go that far.

We sublet the floor above the business premises as a flat. Had tenants from the getgo and no one ever complained about cold or the heating system until our brother moved in. We went into the attic to investigate and found no bloody attic insulation at all!! Elderly grandfather that oversaw the last renovation never checked. Builder is long out of business.

So its bare mortared roof slates with no felt. The mortar has fallen to the attic floor in a few places. The ceilings of the flat are vaulted around the perimeter. ie. When in the attic there is a slope around the edges down to the eaves. About 3-4 inches between roof slates and sloped ceiling of flat below.

I know that if there was a non breathable bitumen felt, I would have to leave 50mm gap in this area to vent the attic from the eaves. However, seeing as there is no felt at all under the tiles can I actually fill this area completely with insulation. ie. 75-100mm and then 300mm everywhere else on the flat area of the attic while also sealing and insulating the attic hatch.

Could the roof members still breath?

It would mean I could do the job myself.

BryanF · 01-11-2013 09:46AM

Calibos wrote: »

seeing as there is no felt at all under the tiles can I actually fill this area completely with insulation. ie. 75-100mm and then 300mm everywhere else on the flat area of the attic while also sealing and insulating the attic hatch.

Could the roof members still breath?

i wouldn't recommend it

canhefixit · 01-11-2013 05:05PM

BryanF wrote: »

i wouldn't recommend it

I know putting felt on is the proper job but what other method would you say would be the best route for me to do?

bryaj · 01-11-2013 08:24PM

If it were mine I would sort the roof covering first - new felt, treated battens & re-slate along with any work to structural members - woodworm, rot etc, with cheaper (that insulated slabs) quilt insulation rolled out in the attic space before insulated slabs or a new kitchen - no point in having things looking good with the roof possibly going to leak.

Have recently renovated an old house that needed major internal work due mainly to roof not having been looked after.

Get your building envelope sorted first.

Markcheese · 01-11-2013 08:57PM

A friend swears by the spray insulation stuff(in an old Georgian house)
When I insulated my cottage roof, I used one of those multilayer foil insulation and it recommended using a vapour barrier but that was below the foil insulation... But fit it carefully,use foil tape to seal seams and edges well ...
Could you just put a membrane on the underside of the roof (up around the joists) and maybe if there is room an inch or two of extra insulation in between the joists and then your insulated plasterboards....

On my place I should have just stuck shelter board (insulated plasterboard) to the existing ceiling cos the whole roof ,timbers and all came off 7 or 8 years later...

GreeBo · 01-11-2013 09:03PM

Why are you trying to insulate the attic?
Keep it as a cold space, insulate the attic floor.
Doing the floor and the roof doesnt make sense.

Then, when you get more cash, re-do the tiles.

Though I'd be getting the roof checked before the winter...a few broken/missing slates with no felt is a recipe for disaster.

Calibos · 02-11-2013 10:04AM

BryanF wrote: »

i wouldn't recommend it

Right then, so how about 50-75mm xtratherm foam insulation board down between the vaulted ceiling below and slates.

ie cut sections to fit between joist/rafters. Slide down slope and sitting right on ceiling plasterboard below. About 50mm between top of insulation board and slates.

Then 300mm insulation roll on rest of attic floor between and over joists.

Am I negating the efficiency of some of the 300mm rolls if the sloped vaulted perimeter only has 59-75mm of insulation board. If so do I just save money and just put 200mm roll down on test of attic and accept that something is better than nothing.

cerastes · 02-11-2013 08:10PM

BryanF wrote: »

if your installing insulated slabs be careful where the due point will be and how the roof space is vented.will you be installing vent slates/vents at the eaves & ridge?drylinign under the rafters, wouldn't be my preferred option.

id say the same about the spray foam, whatever about a new house but one without felt - show me the IAB /BBA cert for its use

Out of interest, if you have a thick enough depth of insulation, which is impermeable on its exterior, does that not push the dew point to the exterior surface? In the case of a roof which should be ventilated on the exterior of the insulation opposed to up against a wall where moisture might be retained in the blocks where it would not be ventilated, would this not be a good thing, i.e. as much thickness of insulation in roofs (as high a value of thermal resistance as possible/practical).
I'm trying to weigh possibilities for possible future work, attic conversion.
Not sure how much detail a draftsperson does regarding insulation or if they'd be aware of what the calculations for heat loss (insulation required) and membranes to prevent movement of moisture.

antiskeptic · 03-11-2013 02:11PM

canhefixit wrote: »

I am starting to do up an old house and in the roof there is no felt at all behind the slates, now i havent the money to get slates lifted and felt fitted so was looking for another effective way to try insulate it a bit better.

There are two ideas going on here:

Felting: this acts as a 'second roof' in case of water ingress past your first roof: the slates. That plus a degree of draughtproofing. It's not meant to be (and isn't) insulation

Insulating: this aims to prevent heat loss.

Felting in itself isn't necessarily critical since a slate roof in good condition (i.e. no cracked/missing slates, chimney flashings in good condition, etc) will keep the rain out on it's own. The felt is a just-in-case. My own 100+ year old roof has no felt and has no problem keeping out the rain.

If the roof isn't capable of this then I'd be attending to it before adding insulation to it.

BryanF · 04-11-2013 09:53AM

Calibos wrote: »

Right then, so how about 50-75mm xtratherm foam insulation board down between the vaulted ceiling below and slates.

ie cut sections to fit between joist/rafters. Slide down slope and sitting right on ceiling plasterboard below. About 50mm between top of insulation board and slates.

Then 300mm insulation roll on rest of attic floor between and over joists.

Am I negating the efficiency of some of the 300mm rolls if the sloped vaulted perimeter only has 59-75mm of insulation board. If so do I just save money and just put 200mm roll down on test of attic and accept that something is better than nothing.

ventilation

BryanF wrote: »

will you be installing vent slates/vents at the eaves & ridge?

bryaj wrote: »

If it were mine I would sort the roof covering first - new felt, treated battens & re-slate along with any work to structural members - woodworm, rot etc,

BryanF · 04-11-2013 09:55AM

cerastes wrote: »

Out of interest, if you have a thick enough depth of insulation, which is impermeable on its exterior, does that not push the dew point to the exterior surface?

yes and into the rafter/timbers that in this case don't seem to be vented

cerastes · 04-11-2013 10:36AM

BryanF wrote: »

yes and into the rafter/timbers that in this case don't seem to be vented

Ok, I see, I read from the OP that they were going to staple some wrap across the rafters, I was assuming this could be considered a vapour membrane if sealed or they would incorporate a breathable membrane with it and that there would be adequate minimum ventilation space and all parts of the structure would be capable of being ventilated.

canhefixit wrote: »

I am starting to do up an old house and in the roof there is no felt at all behind the slates, now i havent the money to get slates lifted and felt fitted so was looking for another effective way to try insulate it a bit better.

I came across a product Therawrap and was wondering would this be a good method were I would staple it across the rafters covering the whole roof, so the attic then looks like its wrapped in tin foil.

Or even if anyone has any other ideas on the best way of insulating this type of roof any advise would be great.

Thanks

Help with trying to insulate roof in an old house

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