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Housing - New Build: Optimal energy efficiency and heating

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  1.  
    • CommentAuthorricedf
    • CommentTimeNov 27th 2007
     
    We are intending to build our house with standard cavity insulation, inslated plasterboard as a drylining, kingspan insulation between the rafters, as much as can be fitted. We are intending to combine this with a wood pellet boiler linked to UFH, ventilation heat recovery system and solar hot water heating. GSHP's at the minute are prohibitively expensive given the grants in the Republic of Ireland and I can install the wood pellet boiler plus solar tubes and hot water tank for £5000 after grants. The boiler I'm intending to use is from a company called Kedco. Does anyone have experioence of this company's products and has anyone combined a wood pellet boiler with UFH and ventilation heat recovery system. If so do you have advice as to a good system to zone and thermostatically control all of this in an integrated way?

    Thanks.
  2.  
    I don't know much about your actual question, I'm afraid. However:

    I wouldn't use insulated plasterboard as a dry lining, for two reasons. Firstly, a dry-lined masonry wall is rarely airtight. Airtightness is more important for energy saving and thermal comfort than a little bit of insulation, particularly as you are having a ventilation system as well.

    Secondly, you're insulating yourself from the blocks. This reduces what they call the "thermal mass" i.e. the heat capacity within the insulation layer. In turn, this makes it hard for your house to store heat from sunlight and, more importantly generally, makes it more susceptible to overheating in summer. I realize Ireland is mild, though.

    Can you not get wet plaster?

    Also, try to put insulation either over the rafters, under them, or both. The timber of the rafters is not very insulative, so it's important to have a layer that it doesn't bridge.

    Have you thought of trying to trade the energy efficiency measures against reduced expenditure capital on heating systems, passivhaus-fashion (my main interest)? Maybe just have ufh downstairs and nothing else? You can build with quite extensive architectural freedom with this setup.
    • CommentAuthorworkaholic
    • CommentTimeNov 28th 2007
     
    ricedf

    You do not give enough detail about your construction to be able to make a useful suggestion. Can you tell us what the leaves of your cavity wall are constructed off? How big is the cavity and what is it filled with? What insulating plasterboard are you using and how is it fixed. It is more important to get the structure correct when you build it. Zone valves and thermostats are easy to fit or replace. The structure is fixed once you build it.
    • CommentAuthorricedf
    • CommentTimeDec 2nd 2007
     
    Full details are: standard double leaf concrete block wall with 100mm cavity and 60mm cavity insulation. It is a dormer construction and there will be 120mm kingspan insulation fitted between truss batons on the second floor and 300mm loft insulation. The insulated plaster board is attached directly onto the blocks on the bottom floor and the batons on the second floor and I was hoping that by using it I would avoid thermal bridging. I had originally wanted to use a litecrete block on the inner leaf of the wall but can't as it won't support the weight of the concrete slabs for the first floor. Windows will be argon filled double glazed warm edge glass with a low-e coating.

    In terms of the thermal mass loss, it has been suggested to me that the ventilation heat recovery system will operate more effectively by keeping the heat inside the space, it must also be said that a certain amount of thermal mass will be stored in the floor and the interior walls which will not be fitted with the insulated plasterboard.

    Thanks.
    • CommentAuthortony
    • CommentTimeDec 2nd 2007
     
    Sounds to me like you floors are thermal ridges and that you are going to be very air leaky.
    • CommentAuthorricedf
    • CommentTimeDec 3rd 2007
     
    Hi Tony

    Thanks for your comment. The ground floor will have the normal 60mm kingspan insulation fitted on top of the subfloor with UFH installed above that and standard screed on top of that. Insulation will be raised at the edges to avoid thermal bridges. The first floor concrete slabs will have the cavity insulation to the outside of them so should be fine. Airtightness is still to be discussed with the contractor. Any other thoughts on this?
    • CommentAuthortony
    • CommentTimeDec 3rd 2007
     
    Parge all the walls before you cover them up -- this is like a thin coat of sand and cement render and very good at reducing air leakages.

    The concrete floor slabs usually have holes in them and these could lead outside air through the floor or into the house.

    The area between the floor and the ceiling needs to be leak proofed

    What happens to the tops of the floor slabs behind the dormer walls? Could they get cold there?
    • CommentAuthorricedf
    • CommentTimeDec 3rd 2007
     
    Thanks again Tony.

    Reckon I'll have to do the best I can with the thermal bridges, get the impression that it's never totally impossible to elimate them in this type of construction. Thanks for the suggestion to parge all the walls prior to boarding, like an airtight(ish) layer below the insulated plasterboard.

    If we fit the upstairs UFH on top of the slab on 60mm insulation as previous then that is probably as good as we can do. There will be some thermal bridging but hopefully the effect will be minimised.

    Damian
  9.  
    Ricedf
    Two skins of concrete blocks and 60mm of Kingspan. What sort of U value does this give? I am amazed it is approved by building control. You say you have an outer skin of concrete blocks, does this mean it is rendered or has some other covering. If this is the case go for a solid wall of lightweight blocks and put the insulation on the inside, or the outside if you believe in thermal mass. Why do you need a concrete 1st floor? You should minimise your concrete/cement use at all costs. There is no problem putting UFH on suspended timber floors.

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