Dormer roof upgrade and fault fixes

Irish Steve

OK, the house was built at the beginning of the 90's, and "on mature reflection" the cowboys that built it trained the people responsible for the more blatant abuses of the Celtic Tiger, so you know where I'm coming from. I will apologise now that this post is not going to be short, but I need to make sure that all the issues have been covered.

We had cavity wall fill done earlier this year courtesy of SEAI, as the original spec was only a thin polystyrene sheet in the cavity, and I'm pretty sure that the original fit was less than comprehensive. Even though it's not really cold yet, I think it's helped, but there's a way to go yet, and finance, or lack of it, dictates that the next job has to be done sooner rather than later, I really do need to get the oil bill down to a more sensible level

Now, the fun starts, as it's time to try and sort out the roof, which is dormer, and to add to the pain, there's 11 Velux windows and a 3 flue chimney in the back face, south facing, and they are causing problems as well. There is also an issue with the quality of the felt that was used, and it's now starting to leak in several places, so water is getting on to the ceiling of the ground floor, so it has to be sorted.

At present, there is some fibreglass insulation in the ceiling joists, and not long after we moved in, I did a major upgrade to put a lot more fibreglass insulation into the walls of the dormer area, and yes it was a horrible job, but it did help make the dormer (bedrooms) almost habitable temperature wise in the winter months.

There is however, no insulation under the dormer floor, and although I've put blocker boards of polystyrene in to the joists, they are far from airtight, and at roof level, it's an (old) traditional felt and batten job, not particularly well done, so nowhere near draught proof. That is allowing a lot of heat to escape, not helped by the added complication of a lot of downlighters fitted in the ceilings of the ground floor, so breaching the plasterboard.

My thinking is that I will line the inside (underside) of the roof rafters with corrie board (8 x 4 sheets of white advertising board plastic cardboard, if that makes sense), held up using thin battens on the rafters) in all the accessible places, (the crawl spaces are large, and used for storage) with sealing tape on the joints

The area to then be addressed would be where the plasterboard is on the underside of the roof rafters, and at the wall and ridge, which I would hope to address during phase 2, which is a massive job, but I don't see an easy way round it, gable end, fascia and soffit boards are all going to have to be replaced, so my plan is to replace them with OSB supports, then plastic fascia and soffit, and at the same time, the tiles, battens and felt are progressively stripped, the air barrier on the inside is sealed to the wall/fascia, the joists in the area of plasterboard, and at the ridge as appropriate, with more corrie board and copious applications of draught sealing tape, working from above, so we don't have to damage any of the plasterboard in the rooms, then the rafters are filled with a suitable insulation, a sheet of OSB is put externally on top of that lot, then a raiser batten on the line of the rafters, tyvek membrane across them, then battens, then put the tiles back on, and work our way up the roof.

Yes, I will need ventilation on the hot side of the vapour barrier under the ridge, but I can get to those areas to fit them, and that will be a case of putting an appropriate vent through the wall with a suitable core drill.

The OSB will gain me some space that will allow the flashing round the Velux windows to be correctly supported and re fitted, they were not well fitted originally, so water gets over the edges of the flashing on to the felt, which is now causing problems.

This plan also means moving the lead flashing round the chimney, which won't be a massive hassle as I've already had to reflash part of the chimney before to solve water penetration issues, and the OSB will provide a better sub base support than is presently there.

After that pain, the front (north facing) side is easier, there are 2 valleys to deal with on a forward facing extension, but the same principle applies, but no windows.

So, the questions.

Is Corrie board suitable for use as a vapour barrier, it has the advantage of being cheap, provides good support to the insulation, and is easy to work with in restricted spaces, and should take draught sealing tape relatively easily,

I can get somewhere around 230 mm of insulation into the rafters, which type of insulation is likely to be best, a "glass" type, pellets or a more rigid "foam" block type, or it it worth considering a spray type insulation?

The plan will be to fill to the top of the rafter, effectively the underside of the OSB, and the corrie board will provide the other limiting edge.

The horizontal gaps between the rafters are supposed to be the same (nominally 610mm all the way, but I know from painful experience that they are not, so foam blocks may be a problem as unless they are each custom cut to width, there may be gaps, which will not help the heat retention. To assist with draught proofing, I'd also tape the OSB joins to prevent leakage there once the sheets have been fastened down

After that, it should be relatively straight forward, vertical batten on the rafter centre lines to get air space above the OSB and under the tyvek, then a normal batten system for the tiles.

In theory, if I've got this right, this gives me a vapour barrier on the underside of the rafters, insulation to keep the heat in, and a draught proof barrier (the OSB) under the roof tiles, which should make a significant difference to the heating bills.

Is this overkill, and have I missed anything.

The roof length is about 22 Mtrs, and front to back distance (not the ridge height distance) is about 10 Mtrs, so we're not talking a small roof here.

Unfortunately, between reading here and spending a long time thinking about this, I don't see any other way to sort the multiple issues with the roof once and for all, anything less than stripping and refitting the tiles battens and felt won't solve the problems in the long term, and if I'm going that far, then it makes economic sense to do the insulation and draught proofing at the same time, the additional cost should be recovered in heating savings.

That said, I'm very open to alternative suggestions or ideas, with the very clear requirement that insulation, draught proofing, and water proofing of the roof and veluxes are all issues that are unacceptable at the moment, so the fix has to address them all.

The one suggestion that will not be entertained is to talk to the original architect, he was in the pocket of the builder, and caused us much grief by signing off on a number of issues that have subsequently come back to haunt us, so talking to him is not an option, and I have to confess to being very reluctant to trust some of the "professional" trades like architects, I'm not sure they've really put their house in order after the Celtic Tiger years, and my personal experience with some other "professionals" like accountants and solicitors have been less than satisfactory, so I am afraid I am very wary of these areas.

Thanks for hanging in there and reading this horror story.

MicktheMan

Would you not be better off converting the roof from cold to a warm roof? I'd be fearful that if you do what you propose you may end up having to replace your roof timber structure in no time due to rot.:eek:

This is a major undertaking you're considering and would advise to get a recommended "professional" to advise irrespective of previous experiences.;)

Irish Steve

MicktheMan wrote: »

Would you not be better off converting the roof from cold to a warm roof? I'd be fearful that if you do what you propose you may end up having to replace your roof timber structure in no time due to rot.:eek:

This is a major undertaking you're considering and would advise to get a recommended "professional" to advise irrespective of previous experiences.;)

Effectively, that's what I thought this concept was, a vapour barrier on the inside of the timbers, a 230mm layer of heat insulation, a draught barrier, and then the weather proofing.

I'm well aware of the size of the job, I'd prefer not to have to do it, but if I don't, the problems are only going to get worse, which is no help. Some of the comments here about draught proofers and insulation contractors are no encouragement in that respect, and we had to get the SEAI cavity insulation installers back to sort out the vents they'd fitted, as there were issues there, hence my reluctance to be trusting.

The problem is finding a recommended professional that will provide impartial and accurate advice. The SEAI site is not much help in that respect, long on ways to spend a lot of money, but short on ways to achieve results, especially where dormers are concerned. The draught proofing and insulation standards that were applicable to dormers back in the day are effectively zero, and with energy prices the way they are, ignoring the situation is no longer an option, despite getting a BER C2 rating after the cavity insulation was fitted.

beyondpassive

To do it right you must either take off the slates and use a sarking insulation board or else take out the finishes in the first floor and take out the plasterboard ceiling along the perimeter of the ground floor. The real problem with dormers is the drafts through the crawlspaces and dormers, in order to get the menbrane to work it has to be continuous. you have to crack alot of eggs to do it right. There are plenty of compromise solutions, but I'd look at the 'top notch' job first.

Irish Steve

The plan is to remove the slates, battens and felt, as the felt on the south side is shot anyway, and then have something like an OSB sheet on the top of the rafters, and that route also means I get to sort out the bad fit of the Velux flashing, which is also causing issues.

My main concern is the combination of heat retention and draught proofing, in that too many people I've talked to seem not to understand the difference between the 2, and as a result, they are proposing inadequate solutions.

MicktheMan

Irish Steve wrote: »

Effectively, that's what I thought this concept was, a vapour barrier on the inside of the timbers, a 230mm layer of heat insulation, a draught barrier, and then the weather proofing.

This is not a warm roof and if done as you describe then the risk of moisture build-up and rot in roof timbers is very high. This is why you need a competent professional advising.

Irish Steve wrote: »

I'm well aware of the size of the job, I'd prefer not to have to do it, but if I don't, the problems are only going to get worse, which is no help. Some of the comments here about draught proofers and insulation contractors are no encouragement in that respect, and we had to get the SEAI cavity insulation installers back to sort out the vents they'd fitted, as there were issues there, hence my reluctance to be trusting.

Caveat emptor! Anybody getting any trade to work on their home need to be clued in and if not then have somebody who is on their side. In this respect, grants can and do cause the homeowner to drop their natural scepticism just because the contractor is authorised by a quango.

Irish Steve wrote: »

The problem is finding a recommended professional that will provide impartial and accurate advice. The SEAI site is not much help in that respect, long on ways to spend a lot of money, but short on ways to achieve results, especially where dormers are concerned. The draught proofing and insulation standards that were applicable to dormers back in the day are effectively zero, and with energy prices the way they are, ignoring the situation is no longer an option, despite getting a BER C2 rating after the cavity insulation was fitted.

Forget SEAI, BER rating etc and talk to someone who has actually converted a draughty cold house into a healthy, comfortable and affordable house.

Look, there are so-called professionals who are still in the stoneage wrt building physics and energy efficiency but there is also a lot of highly qualified independent and experienced professionals out there who can advise appropriately and professionally.

Irish Steve

MicktheMan wrote: »

Look, there are so-called professionals who are still in the stoneage wrt building physics and energy efficiency but there is also a lot of highly qualified independent and experienced professionals out there who can advise appropriately and professionally.

Indeed, which is one of the reasons I've posted here, I will be happy to get PM's recommending companies that have done a good job at reasonable prices, and I will be looking very closely at this before doing any actual work, it's too big a job to get wrong, and mistakes on this scale tend to be expensive. The mechanical structure of the roof is fine, fortunately, it wasn't designed by the architect or the builder, it's pre made trusses, and there are no issues with any of the underlying structure, the problems are all related to the way the builder finished things off once they'd got the trusses in place. Poor quality felt not well laid, Velux flashing not properly supported, lead valleys not correctly supported, I'm sure you've seen it all before. The architect should have picked up some of the issues, but he didn't, hence my comments earlier.

It will get sorted, and I'm sure that it will make a significant difference to our heating costs, as well as reducing maintenance issues. That has to be good, for a lot of reasons.

MicktheMan

Irish Steve wrote: »

I will be happy to get PM's recommending companies that have done a good job at reasonable prices

There is a sticky in this forum for exactly that.:)

galway1973

What about the spray foam option. They can now access through the plasterboard.they say its breathable. Was thinking of getting this done myself.

MicktheMan

Is the product and application method certified?

galway1973

MicktheMan wrote: »

Is the product and application method certified?

As far as I know

MicktheMan

galway1973 wrote: »

As far as I know

galway1973

MicktheMan wrote: »

BBA cert
ETA approval
IBA cert

galway1973

MicktheMan wrote: »

BBA cert
ETA approval
IBA cert

angelclar

i got sprayfoam completed in my home . by a company <snip> they installed a vent tray system to prevent dry root .
Its part of the NSAI standards the sales rep said .

i have found such a differnce in my home for heat storage

bjfmd

im thinking of doing the same job, sprayfoam, my dormer is slabbed we are living up there for the last 6/7 years but its freezing as soon as the heating goes off, how much slabs would i need to remove to get sprayfoam between the rafters ??? thanks in advance for any advice...

BryanF

Ring a manufacturer of spray foam NOT an installer. They will tell you you need vent cards in all area under the felt and possibly Vapour barrier on warm side behind plasterboard. Do not trust the installer, unless they provide you with the CE/iab/BBA cert only as there is a lot of false/ misinformation around re spray foam attic ( & cavity insulation)