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General: flat roof insulation

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  1.  
    • CommentAuthorsnowy1988
    • CommentTimeNov 9th 2007
     
    We have just had a Firestone EPDM roofing system installed to new plywood flat roof. This will form the roof over a new staircase, part of a major renovation project. We thought that we were getting insulation and vapour control layer installed under the EPDM but what we have got is the EPDM fixed directly to the ply. Can anyone advise the best materials to use under the flat roof to achieve good insulation and vapour control layer?
    snowy1988
    • CommentAuthortony
    • CommentTimeNov 9th 2007
     
    The best? Polythene makes an OK vapour barrier so would platinum foil.

    The roof will now have to a cold deck roof so how deep are the bits of wood?

    My ideal and cheapest would be 300mm of quilted insulation with a 50mm ventilated air gap between it and the deck.
    • CommentAuthorsnowy1988
    • CommentTimeNov 9th 2007
     
    Thanks Tony.The joists are 7" and the firrings above these are 0-3".
  4.  
    Snowy,

    If it is above heated accommodation my advise is don't pay them and get your local building inspector involved. They maybe liable for not advising you about the building regulation requirement PART L1 B 2006.
    Your room will always be colder than it should be due to the failure of this roofing company. Moisture will be attracted to the cold deck and will condense and in a few years you'll end up with a rotten roof.

    Tony is right but is it feasible at this point to provide a 50mm through ventilated air gap? Also you'll probably struggle to get enough insulation between the joists to meet building regulations. It depends how deep the joists are. Another option is an inverted roof (insulation on top of the membrane) but allow an extra 50% thickness in insulation for heat loss because of water infiltration and you'll need 2 inch paving slabs on top of the insulation with lead flasihing on the ends. You would have an increased loading on your roof.

    My company install flat roofs and always advise a warm-deck roof above heated accommodation because we would liable for the situation you are in.

    I always check with insulation suppliers technical department for latest advice to meet building regulations and pass this information on to the customer. All this information should be given to you pre sale.

    There is also a possibility that the roof could be raised in a survey for not meeting building regulations. Cold roofs are banned in Scotland.

    Cheers

    Steve
    • CommentAuthorSaint
    • CommentTimeNov 9th 2007
     
    Snowy, no question unless there's an issue of space, go for an inverted roof build up or USD (upside down roof). Extruded polystyrene insulation can be placed directly on top of the EPDM, yes externally so the EPDM remains untouched. This creates a warm roof, throws the dew point outside the structure so there is no chance of interstitial condensation and long term protects the membrane from trafficking, UV and solar gain.
    Two ways to keep the insulation in position. One if the roof can take the load then its simply ballasted to the same thickness as the insulation boards themselves. two if the roof cannot take the load then go for a lightweight solution which has the extruded polystyrene with hT&G jointing rather than shiplap with a 10mm modified cement screed on it. This can be secured in place by adhesion or just loading the perimeter boards with paving slabs 450 x 450 x 50 will do but check prevailing wind. Suppliers won't sell the products unless the know the height, orientation and shape of your roof.There are a few suppliers of XPS for USD roofs, try Dow Styrofoam Roofmate, Knauf Roofboard, can't remember the Kingspan one but its probably based on BASF's Styrodur if its a green foam, otherwise its Styrofoam, Ursa XPS or similar.
    For the lightweight varieties there is Dow's Roofmate LG and Styrodur's Chevron, now marketed by Kingspan.

    Look upon this as an opportunity not a problem. I did one of these on my house a few years back and it worked fantastically
  6.  
    Hi Snowy, I would not contact Building Control as they may make you install the required level of insulation which is now very difficult. The issue of responsibility is also tricky as the contractor is only responsible for what you, as the client, have instructed or agreed prior to the work bieng carried out. Ie, if you have agreed on say 300mm of mineral wool, then that is what should have been done. However, I do not think Building Control will not get involved in any dispute as it will be a civil matter between you and the contractor. What they may do instead is to require YOU to rectify the work [how you recover your costs bieng your problem]

    Can I ask if the roof is ventilated in any way? This is the Critical point in deciding which will be the most effective [and cheapest] way forward.
    • CommentAuthorsnowy1988
    • CommentTimeNov 9th 2007
     
    Hi Mike
    The roof is not ventilated. Building Control will see the roof anyway because they will be inspecting other work we are doing. The problem arose because we were referred to this contractor by a Firestone rep who sent our architect information about the warm roof system. We thought this was what we were getting but it has turned out the quote was only for supply and fit of the EPDM.
    Snowy
  8.  
    Hi Snowy, After thinking more on this it may be that the EPDM is only loosely laid and not mechanically fixed at all. See http://www.delston.co.uk/epdm.htm

    If so, can it be rolled up and relaid on top of a newly insulated deck? This would then be in accordance with the practice outlined at delston above. Otherwise Saint's suggestion may be the cheapest and best way to go. Mike
  9.  
    I've a 1950's house with a flat roof outbuilding that I'm going to use as an office. There seems to be a lot of conflicting advise out there, does anyone have experience of taking a mostly waterproof concrete flat roof and converting it into an insulated (insulation on top of the flat roof) and waterproof roof? I don't want to take the concrete off and if I can get away with it, I don't want to attempt to remove the existing asphalt layers. A green roof would also be good here - but I want to keep costs under control.

    My key concerns at this stage are: planning (as all options seem to change the height of the roof; skills (there is only me to do this so anything requiring specialist skills is out); and insulation/water proofing. Thoughts?
  10.  
    Hi Adrian, I looked at using EDPM recently but chose not to because I wanted to see an example of the finished article. Unfortunately, the company I contacted did not want to disclose their customers' adressess. Since then I have learned a little more about the system and it does seem to be a good DIY option. One important thing I have learned is that the EDPM shrinks initially, meaning that you have to loose lay it for a period of time before finalising the work. See also http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=632&page=1#Item_10
    • CommentAuthortony
    • CommentTimeNov 11th 2007
     
    Adrian, how will you join up your roof insulation to that in or on the walls? You may finish up with massive thermal bridging negating the insulation that you do.
  12.  
    The plan was basic external insulation to the whole building (wooden clad to match some existing sheds). Does raise an interesting point though - one of the walls is on the boundary for a neighbours property - can I actually insulate that wall with the risk that I may encroach over their land?
    • CommentAuthorMike George
    • CommentTimeNov 11th 2007 edited
     
    Posted By: tonyAdrian, how will you join up your roof insulation to that in or on the walls? You may finish up with massive thermal bridging negating the insulation that you do.


    Isn't that a bit of an exageration? Surely insulating the flat roof is a great idea regardless of any thermal bridging.
    • CommentAuthortony
    • CommentTimeNov 11th 2007
     
    Talk to the neighbour -- you might need to do fireproof insulation? -- best idea is no thermal bridges.

    Roof could be as simple as eps on top of what is there then boards fixed then waterproofing layer.

    I once saw a waterproofing layer of one layer of cheapest black felt not stuck down or fixed with 25mm of stones in it never leaked for 60 yrs. fall was 1 in 35

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