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Dormer insulation options

  • 18-11-2017 6:03pm
    Registered Users Posts: 17

    Hi all,

    Have got a few different quotes and options for insulating my dormer house which I bought this year.

    The house was built in 2003 and has aero board in the walls and rock wool in the crawl space and attic space. The slope of the dormer has a yellow foam board, don't know what this called.

    The house doesn't retain any heat. We could have the oil heating on for 3 to 4 hours and once it's turned off you can also start to feel the place getting cold again. The house is ok with the heating on but wouldn't be strolling around in shorts and a t shirt... Radiators are hot when it's on. So heating while can be improved is not the main issue. The crawl space is seriously cold.. And believe this is the main root cause.

    And also have spoke to a few companies about heating improvements and all say sort the insulation first, otherwise it's a waste of money.

    So my options...
    Company 1)
    In the walls use walltite cv100. He doesn't believe the beading will make a major difference as the aero board is away from both walls... So gaps will be left if beading used. The walltite will push it back in, the beading won't. Big price difference in both.
    For the roof, just use spray foam in the crawl space.

    company 2)
    Forget about the walls for now, do the roof and the re assess.
    For the roof, remove the yellow board and use spray foam the entire lenght of the roof. From the wall plate/facia up to the apex and down the other side.

    Company 3)
    Use beading in the walls, he thinks the walltite is too good.
    For the roof, use spray foam in the crawl space and attic space. Leave the yellow board in so just use the spray foam in the bottom third and top third of the roof.

    So 3 different approaches, so looking to see which is the best. To note all 3 use the card and leave an air gap of 50mm which is required when using spray foam.

    Any success/failure stories with spray foam also? Appreciate any advice.



  • Registered Users Posts: 93 ✭✭Charlie 08

    Any update/progress made on this? About to embark on a similar project myself...

  • Registered Users Posts: 254 ✭✭Pious14

    Would also be interested in an update. Have dormer but can’t sccess the roof to insulate with out removing slates

  • Banned (with Prison Access) Posts: 1,934 ✭✭✭robp

    I am not knowledgeable on the topic but I think airtightness is a key feature of ensuring a warm house. I am not sure if using spray foam alone is a very direct way of improving airtightness.

  • Registered Users Posts: 1 Brenlizzy

    Anyone make any progress with insulating their dormer? We're in the same boat right now, confused with all the different options.

  • Moderators, Home & Garden Moderators Posts: 10,133 Mod ✭✭✭✭BryanF

    Brenlizzy wrote: »
    Anyone make any progress with insulating their dormer? We're in the same boat right now, confused with all the different options.


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  • Registered Users Posts: 17 Jimmywangyang

    Hi All,

    Haven't logged into this in a while so only seen some of the responses now.

    We ended up going with what Company 3 had outlined. So pumped beading into the walls and the plan was to remove the yellow board insulation and spray foam the full roof, when they guys checked there was actually 2 layers of it, and it was jammed in!

    So we just done the crawl space and attic space with the spray foam.

    The difference in the house is crazy, but i think the insulation was so poor before we done this that any insulation would have improved it. For example the conservatory had absolutely no insulation, in the walls or roof!

    Before if you stuck your head into the crawl space the breeze would nearly cut you it was so cold, now there is no breeze.

  • Registered Users Posts: 93 ✭✭Charlie 08

    About time I updated also.We also used foam in our dormer recently. crawl space and upper attic sprayed. We removed the aeroboard that was in the slope area and spray foamed this also. Just like the previous poster, It has made a huge difference with the upstairs occupants complaining that it's too warm at night time!!

  • Registered Users Posts: 22 jimbojonez

    Thanks for the update guys, have a 15yr old Dormer myself and considering spray foam insulation for attic and crawl space, how much did yours cost, if you don't mind me asking.

  • Registered Users Posts: 49 abbey

    Reading the above with interest.

    We too are interested in improving the comfort level of our 15 year old dormer. It was suggested to us that an alternative to spray foam was Super Quilt.

    Has anyone used this to insulate the rafters in their dormer attic spaces? If so, how do they find it? Is it useful in cutting down on draughts?

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    I always advise all my clients that they should not use Spray Foam insulation in the Attic

    it will not stop all of the heat losses by draughts (Convection)

    1. Heat is lost from a house is by either (a) Conduction or (b) Convection. 
    2. CONDUCTION is heat loss through an element of the structure:- wall; ceiling; floor; windows, etc
    3. you should be able to see the insulation in the attic, which should be approx 300 thick in the horizontal and approx 100 mm thick on the vertical.
    4. double glazing gives a good U value in relation to heat loss. 
    5. CONVECTION is heat loss by the movement of air
    6. Some builders and some workers on site are a disgrace to the Construction Industry, and do not have the proper knowledge of correct construction, and some are just totally incompetent and don’t care.
    7. There are 5 main areas in most houses where air is exchanged between the house and the attic void, especially in older houses. (A) holes in the ceiling of the hot press where the pipes from the plumbing and heating pass through at this point. (B) Attic access doors that are poorly fitted and are not fitted with draught excluders. (C) Where the electric wires from the attic void pass down through the ceiling to the Fuse Board (consumer electrical distribution board) and (D) through the holes in the ceiling where the electric wires pass down through the ceiling to the electric light fitting in every room. (E) Downlights that are not air sealed above the ceiling, and /or not properly sealed below the ceiling and 
    8. also draughts around enternal windows and doors, between the frame and the internal plaster. 
    9. To reduce heat loss and draughts and reduce the amount of condensation getting from the house to the attic these holes should be completely blocked and made air tight. 
    10. Downlighting should be replaced with sealed units. 
    11. Health & Safety. Only persons competent in walking in the attic, should go in to the attic to carry out the sealing of these holes. No person except a competent electrician should open any electrical fittings.
    12. Expanded foam should only be used by competent persons and strictly in accordance with the manufacturers safety instructions. 
    13. All of these holes could be sealed with silicone mastic —-( would be my choice of sealant.) For large gaps it can be built up over a few days. 
    14. The attic access door should be fitted with a rubber draught excluder with some fittings to compress the rubber (screws). Also put 100 minimum Insulation on the upper side of the access door (could be glued on with silicone mastic). 
    15. Rooms in the Attic would have other gaps and are notorious for draughts and air leaks which are not mentioned above.
    16. where the plumbing pipes pass through the ceiling in to the attic is usually an area of big heat loss. 
    17. have a look at the areas of heat loss by Convection that I have mentioned above. 

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  • Moderators, Motoring & Transport Moderators Posts: 6,510 Mod ✭✭✭✭Irish Steve

    In no particular order,

    The house here is a dormer bungalow, 32 years old, and traditional construction, but the words I've used to describe it is that we had a period of construction in the noughties that were built by Celtic Cowboys, and the builders that built our part of the estate were responsible for training the Celtic Cowboys, and 30+ years ago, the levels of supervision and accountability for complying with the even poorer standards that were in place at that time was effectively zero.

    So, this house was COLD, despite having a well specified oil heating system, and after the first winter, I went investigating to try and work out why.

    It wasn't hard. The builders has massively skimped on the fibreglass insulation, like putting nothing in to the internal walls on the upper floor, and there was a massive issue with there being no sealing or insulation to prevent the winds that came in from outside from howling straight through under the upstairs floor, and going out the other side and taking a lot of heat with it. 19 Rolls of fibreglass later we had as much as we could of that issue resolved, but there were places where it wasn't possible to get fibreglass in.

    The ends of the joists under the internal walls were not closed, and there was no insulation under the upper floor, and to make things worse, all the lights in the downstairs celling were halogen downlighters, and of a design that was very much NOT airtight. The draughts through the downlighters was only massive, so the first job there was to get a large number of catering size (baked bean) tins from a local coffee shop, and fit them over all the accessible downlights to seal the gaps while keeping the insulation away from the lights, the transformers were put on top of the tins to make sure they stayed where they were put, and to keep them out of the fibreglass. The ends of the joist under the internal walls were closed with polystyrene sheeting, and the internal walls were also fibreglassed to improve their insulation. That made a significant difference, but there was still an issue with wind in the crawl spaces that made things difficult, but at least now it was possible to get the house warm when we needed it to be, but it was clear that there were still issues. Oil wasn't a massive price in those times, and there were no easy options to improve things.

    Roll on to more recent times. SEAI had a scheme for pumping beads into cavity walls, which we qualified for, and while there was polysytrene sheet in the cavity, the pumped beads made a difference.

    In early 2020, all the downlighters were taken out, and replaced by a much better fitting LED light that sealed the gaps, so no more draughts through the ceilings, and a significant decrease in the electricity needed for lighting, there were 9 halogen lights in the kitchen alone, and the LED's reduced the demand there from 450W to 63W, as well as sealing the gaps.

    We were looking at maybe a heat pump in 2020, and as a prequalification, we had a BER done, and it came in as a C1, to improve on it was going to need several big ticket projects, so the heat pump went on hold, and we've concentrated on other issues to improve things.

    The most recent change has been to get the roof foam sprayed, and that has been a massive improvement, it was evident within hours of doing the job that the winds were for the first time no longer getting into the roof, and taking the heat with them. Effectively, the foam has provided the draught sealing that was needed to retain the heat, and we've very much noticed a massive difference in the temperatures in the upper floor, in both directions, it's cooler in the summer, and was warmer during the winter, most of the time without having to put the radiators on the upper floor on at all, and our oil burn this winter has been significantly lower, partly because it's been a milder winter, but also because there are not the draughts sucking the heat out.

    It's also quieter in the upstairs rooms, while that wasn't as such a selling point, being under a Dublin Airport departure and arrival route, the noise reduction has been helpful.

    As an experiment, we also changed one window and reglazed the patio door with lower value glass, and that's driven a decision to now replace all the windows later this year with new units, while they were double glazed, the energy loss through them is significant, and we noticed a difference in the 2 rooms that were upgraded, so it wasn't hard to see the potential benefits to be gained from doing all of the windows and doors.

    The biggest change from all of the above was to get the roof sprayed, the crawl spaces are relatively small, as is the space above the dormer rooms, but the difference has been massive, and that's down to stopping the free movement of air that came in through the fascias and took the heat with it on the way out of the other side. The crawl spaces don't get that hot as such, as the fibreglass on the ceilings did a reasonable job, but there were too many places where it wasn't possible to get good insulation, and the draughts took full advantage of that. Now, with some careful preparation before the spraying was done, the draughts are gone, completely, so that's made a huge difference. The roof here is large, 20 Mtrs x 7. with an extension on the front, so close on 300 Sq mtrs of tile area, it wasn't possible to spray the whole area in one day, but it wasn't a full 2 days to do it, and the lads that did the job were good, and left the place tidy after they'd finished, so we were very happy with the end result.

    Hope that helps some of the people asking, it's taken a long time for appropriate options to become available, and we're not completely there yet, but we're in a much better place costs wise than we were, which is just as well given what's happening at the moment with energy prices.

    Once the windows and doors are done, we then are considering removing the one remaining open chimney to reduce the air changes, and I suspect that all of the other changes since the 2020 BER should bring us to a high B rating, and if we were to then add some Solar PV, that might even get us into a low A rating, and help with the ongoing electricity costs.

    As for a heat pump, that needs some newer technology for us to go that route, underfloor heating is not an option, I don't want the hassles of tearing out over 200 Sq Metres of tiles, the cost of doing that, and reinstating afterwards with new floor covering is just too much pain, and new radiators throughout would push the costs way up, so that's going to have to wait.

    Shore, if it was easy, everybody would be doin it.😁

  • Moderators, Motoring & Transport Moderators Posts: 6,510 Mod ✭✭✭✭Irish Steve

    Shore, if it was easy, everybody would be doin it.😁

  • Moderators, Recreation & Hobbies Moderators, Social & Fun Moderators, Society & Culture Moderators Posts: 6,887 Mod ✭✭✭✭shesty

    Reading with interest as we have a 1960s dormer that eh...evolved... over the years.We moved in late last year and have had a very cold few months.

    We are going to go with external insulation most likely.The evolution of the house, and the way it was constructed suggests to us that pumping the walls may not be straight forward and therefore, not worth the attempt.

    First off we have put in the correct size boiler, and changed over to natural gas.Significant difference in how quickly the house heats up.Secondly we are in the process of putting a PVC composite front door and a PVc back door.This has made a huge difference in the hall, and take all the drafts out of it.

    Neither of us are keen on spray foam, as there is a suspicion it may cause rot on roof timbers over time (we work in construction), but reading the above, I think we will need to consider it for awkward to reach parts of the attic, - and there are a few of those.

    We recently bought an insert stove for the fireplace - blocks the chimney but you still have a fire.We had one in a previous house and loved it.

    I fully agree on blocking up access hatches to the attic with insulated board or similar behind a door,as this is a very effective way to cut off draughts.

    We will eventually do all the windows also.And eventually change to a heat pump, but not until we have done a good bit more on insulating.Among other things.

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Many people are having external insulation fitted to their homes.

    All the Retrofitters will advise them that it’s the best thing to do. And it is the best thing for them to take as much money that they can get from the home owner and do a little work as is possible in a very short time.

    Unfortunately when heat loss from the house gets into the cavity, the heat will rise up in the ventilated cavity, and escape through the top of the open cavities.

    Meanwhile, the external insulation is waiting outside and wondering - when is the heat going to come out. 😂😂😂😂😂😂😂

  • Moderators, Recreation & Hobbies Moderators, Social & Fun Moderators, Society & Culture Moderators Posts: 6,887 Mod ✭✭✭✭shesty


    A fair point.We were only discussing this evening, we will internally board some of the walls as we do work on them in the coming months, with insulated board.

    We also have suspended floors downstairs which are pretty much just wind tunnels!Not quite sure what is under there yet, but it may warrant filling with some sort of insulation too.We will lift a few boards in the next few weeks and see what is going on.

    All of this is very money- dependent here obviously.

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Insulating the external walls, is a good method of reducing heat loss by Conduction.

    Your house was constructed in the 60’s, so it is possible that the external walls are constructed with 225 mm Cavity concrete Blocks, with 2 cavities in each block. This wall is referred to as a Cavity block constructed wall. (Or hollow block Constructed wall)

    100 mm block outside with a 50 mm cavity and a 100 mm concrete block/timberframe inside wall is called a Cavity constructed wall.

    The external walls of your house may also be s 225 mm solid concrete blocks.

    The U value of these walls will be a heat loss of approx 2.1 watts/ m2 / degree C/ hr.

    The cavities in Cavity blocks must Never be filled with any insulation.

    Both the Cavity Block wall, and solid concrete block walls can be Insulated Externally or Internally.

    Internal insulation approx 65 mm + 12 slab fixed internally will meet the Building Regulations (BR) to give a U value of approx 0.35 Watts / m2/degreeC/hour. (On any of the 3 types of walls mentioned above.)

    This will reduce your heat loss by conduction to 1/6th.

    This will allow you to do 1 room at a time to suit your budget.

    It is also recommend fixing a slab with approx 20 mm insulation to internal concrete block partitions which are connected to the external walls- because these will become Cold-bridges when you insulated the external walls internally.

    It will also be necessary to fit 10 mm to 20 mm insulation + slab to the 3 reveals of each window. (Assuming a window board).

    I will reply re timber suspended ground floors soon.

  • Registered Users Posts: 49 abbey

    thanks C Eastwood for taking the time to give such a detailed reply.

    Much appreciated.

  • Registered Users Posts: 757 ✭✭✭C. Eastwood

    Shesty and abbey

    i normal advise Clients firstly to insulation the ceiling with insulation on top of the slabs.

    Next insulate the external walls.

    Next fit double glazing with draught proof frames to windows and external doors.

    The floor should be the last to be insulated.

    The best and most expensive job to do on the timber suspended ground floors is to remove all the timber. Block the vents and fit a DPM/ Radon Barrier, put insulation on top of it and pour a concrete floor on top. I would only recommend this if you have plenty of cash.

    Not a lot of heat is lost by Conduction through a ground floor in our mild climate.

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Thanks for your kind comments

    Kind Regards


  • Registered Users Posts: 49 abbey

    Excuse my ignorance.

    When you say 'insulate the ceiling with insulation on top of the slabs' are you talking about in the attic.

    Currently within the attic there is mineral wool between the joists and some laid on top. It's 15 years old, should it be removed and replace with new wool between the joists and across the joists? Or do we install PIR board between the joists?

    We are planning to insulate and draught seal the 4 attic doors in the 2 dormer rooms as you suggested. Is there a particular type of insulation that we should stick to the back of these doors?

    In regards to the gable walls in the 2 dormer rooms there is plaster board stuck onto the outside block. Do we have to do anything to these walls i.e. seal them and replace the plasterboard?

    As regards the ceilings in the dormer rooms, would it be necessary to take down the ceiling board and replace with newer insulated board as was suggested to us?

    Anyone able to advise?

    Thank you.

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  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    The present insulation is fine and leave it in place.

    I would not use PIR, I would use wool.

    Here is a photo of a new flat roof. The wool insulation rolls are on the floor.

    Now the wool is fitted between the roof joists in the next photo

    Next photo shows the insulated slabs fixed with screws and washers to the joists. You can see the ceiling air/ tightness membrane brought down the walls

    This photo shows the roof light with the ceiling slab below - and the edge of the slabs and if you zoom in you can see the insulation and slab.

    You said that there are slabs fixed to the inner face of the gable walls. How thick is the insulation on the back of these slabs. If it’s thin, leave it in place and fit new slabs with approx 50 mm insulation over these slabs. First fit an airtight membrane if it’s required.

    Regarding the existing ceiling slabs of the dormer rooms. If it is possible to fit the new wool insulation above the slabs from the attic, do not take down the existing slabs. Fix an Airtight membrane if it’s required on to the existing slabs. Then fix the new insulated slabs on over the existing slabs with screws and washers.

  • Registered Users Posts: 49 abbey

    Thanks for the detailed reply, with pictures too!

    Very clear to follow for us lay people trying to make sense of the numerous info. sources.

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    Your very welcome

    Thanks for the kind words


  • Registered Users Posts: 239 ✭✭Grassy Knoll

    Thanks to the posters above, some v interesting posts above. My situation is we moved into a 1930 bungalow in 2013 which came with a 1990s dormer conversion plus similar vintage rear extension. On taking possession of the property I was nearly opening the windows to let the heat in it was so badly constructed!

    On a very limited budget and to my regret zero professional advice, we got some builders/ handymen in to do a v small job. We had all the downstairs rooms drylined internally with 100mm insulated plaster boards where possible. (This Works well apart from a few unavoidable cold bridges). Under some of the downstairs suspended floors we had rockwool installed between the floor joists - not ideal but better than nothing. Upstairs in the dormer there was zero insulation between the roof rafters or knee walls. Through a combination of the access through the crawl space and where possible cutting 1 foot wide horizontal slits across the ceiling plasterboard they managed to insulate most of the roof with 100mm rolls. However, it doesn’t work well in the rooms due to a combination of the insulation not being applied universally across all the roof; there not being enough insulation in the dormer ceiling; and a large number of Velux windows which came with the 1990s dormer work. Summer is too warm and winter is cold. The knee walls were fixed and seem good.

    my question is I see above dormer Attics being spray foamed. Is this an acceptable solution for dormers, and to do so properly, are the roof tiles removed to access externally or is there a route in from internally? An issue from internal work is fitted furniture, bathroom tiling and general access are issues. Also are Veluxes a weak point for dormers and are there any views on how to address them. It is remarkable the change and level of awareness around insulation in a relatively short period … any helpful observations most welcome.

  • Registered Users Posts: 2,551 ✭✭✭Yellow_Fern

    In my non-expert opinion warm boards are not the best way to retrofit insulation on a dormer, but they are not a terrible solution either. I wonder is it really an insulation problem. Cold spots are bad, but usually don't prevent a room being heated. Did you notice many draughts? Could be this.

  • Registered Users Posts: 239 ✭✭Grassy Knoll

    There certainly were some draughts some which I hopefully will have rectified for this winter. However, the dormer space is not as well insulated as it should be which causes issues in winter and summer (uncomfortable over the recent heat wave). I suppose some of my efforts have been piecemeal and to be fair a bigger job is required….

  • Registered Users Posts: 2,551 ✭✭✭Yellow_Fern

    Overheating of dormers is common. There are mixed philosophies on this. Some swear by using heavier insulation, like wood fibre blocks, which they say helps moderate the temperature swings. For being too cold in winter, check that upstairs is designed for with the correct sized heating system.

  • Registered Users Posts: 49 abbey

    Hi all,

    Interesting to see what other people have been doing to remedy their draught and cold issues. We haven't done much yet, small kids and life have us still stuck in 1st gear.

    We had a guy out to look at the attic a week ago. Basically as has been suggested by C Eastwood here tidying up the rockwool and laying a new layer of 100mm of insulation alongside sealing the doors and down lighters is the way to go. It was suggested to me that to keep the cost down I should tackle the tidying up part (the messy part as far as I am concerned) myself and then they will do the rest for a princely sum.

    Alongside that it seems you only can obtain the SEAI grant if you tackle the ceilings in the dormer rooms in conjunction with the attic space. Has anyone done this. Am I correct to think this is a messy and expensive job?

  • Registered Users Posts: 2,811 ✭✭✭MicktheMan

    The main heat loss mechanism in dormer houses is air leakage. Your best bet is to have the house tested for air tightness where it is demonstrated to you what is happening and how best to remedy given your budget, future plans etc etc. Not understanding what is going on and how to address it will likely lead to you spending time & money on measures which will have little to no impact on this or, worse, on measures that may well cause significant problems in future years.

    Be careful to not negatively your indoor air quality so a balanced approach is best.

    Finally, don't let the SEAI grant tail wag the heatloss dog. First determine what the issue(s) at play are and only then see if there is a suitable grant to help.

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  • Moderators, Motoring & Transport Moderators Posts: 6,510 Mod ✭✭✭✭Irish Steve

    So, at last, having waited over 9 months for the new windows to be made and fitted, along with new doors, we're about as good as it gets for now, the last outstanding job has been done, and it's another improvement as a result, while the old windows were structurally sound, their seal levels were not great,and 30 year old double glazing didn't do a lot to help keep the heat in.

    We were a C1 BER, and with the changes we've made, since that was done, we should have come up to a more sensible level, and while it's not yet gone cold this year, we're not using a lot of oil, and the heat we're putting in is hanging around a lot longer, because we're not losing the heat through air losses. I tried to get the BER contractor to come back to us to update it, 3 months on and I'm still waiting for his call, so even if he does call now, he won't get any repeat business from me, having done my research, his previous effort wasn't great, so his lack of interest now has put him out of the running.

    As for what to do about oil heating, we'd planned to go over to gas, but that's been put on hold as a result of the ongoing price issues, if I can get a condensing boiler at a sensible price, it might be worth doing, but working out some of those ideas is not easy, the BER system is loaded against letting a house owner "play" with the numbers to see what will work best, and the grant system is very much loaded in favour of giving the one stop shops an even bigger return than they would otherwise make, and we've found that it would have ended up costing us way more to get the grants than it did by going independant of "the system".

    Shore, if it was easy, everybody would be doin it.😁