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Housing - Renovation: insulated plasterboard - but HOW THICK?

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    • CommentAuthordwalker
    • CommentTimeJun 15th 2008
     
    Hi all,

    We own a 200 year old SMALL detached house with solid 18 inch stone walls.

    Its such a cold house in winter. So to improve things I am considering adding insulated plasterboard, but how thick does it need to be to make any marked improvement. Yes, having read several other posts here and on other forums, so I know "the-thicker-the-better" but...

    I want to know if I added say 27mm insulated plasterboard to the internal walls would that make a significant energy saving?
    Or would it be a waste of time/money?

    Also, would it be feasible to fix insulated plasterboard straight to the existing plastered walls?
    (using no wooden batons, thus minimising space lost and work done)

    I would be greatful for any information on this

    Thanks

    Dave
    • CommentAuthortony
    • CommentTimeJun 15th 2008
     
    You can fix straight on. But you will have cold bridges at the internal wall junctions etc.

    Can you consider external insulation?
    • CommentAuthorMike George
    • CommentTimeJun 15th 2008 edited
     
    50mm PUR laminated to 12.5mm Plasterboard is what I have used in upgrades - any thicker and it becomes difficult to fix with screw fixings. Very effective if a lot of attention is paid to air tightness as well. Search here for dot and dab thread. I use adhesive and mechanical fixings.

    Around £35 per board [2.4x1.2m]

    Any insulation is better than none and it is the initial bit which is most effective. Doubling the thickness does not double the saving - there is a law of diminishing returns with insulation.
    • CommentAuthorSaint
    • CommentTimeJun 16th 2008 edited
     
    Dave,
    As Mike has suggested with 50mm PUR and 12.5mm plasterboard you’ll reduce the wall U value from around 2.1 to 0.4W/m2K or so.
    That’s giving you an 80% saving through the walls which is tremendous. On your property though I’d imagine that if using a rigid foam thermal board you’ll need to use timber battens so the total build up will be in the region of 85mm.

    Alternatively Aerogel will give you a few thin choices, the first would be a 2 layers of 10mm option ready bonded to plasterboard or Fermacell, this would take the U value to around 0.52W/m2K thus giving a saving of 75%. Both solutions can be fixed directly to the wall. Applied thickness is then 30mm.
    A utility company is supporting the Fermacell option with funding through the CERT scheme so that could be very cost effective.

    Another solution is to use a single layer of 10mm Aerogel with wet plaster, that would give a U value of 0.8W/m2K and a saving therefore of 60%.

    Soon there will be another option with Aerogel available in thin flexible boards/sheets that would be applied like wallpaper. These can be adhered directly to the wall with wallpaper adhesive whilst the face of these flexible boards will be pre-finished to receive either paint or wallpaper. Again a single 10mm layer would give a saving of 60%, a double layer of 10mm 75%
  5.  
    Saint, battens are not necessary with my method either.

    I still haven't used aerogel yet because of the cost, though with oil prices going up all the time it may not be long before aerogal will be most peoples product of choice. I would certainly use it where budget permits.
    • CommentAuthordwalker
    • CommentTimeJun 16th 2008 edited
     
    MANY THANKS FOR ALL YOUR RESPONSES

    This is exactly what I suspected:
    Posted By: Saintyou’ll reduce the wall U value from around 2.1 to 0.4W/m2K or so.
    That’s giving you an 80% saving through the walls which is tremendous
    and am glad to hear it. So now it has spurred me on to get on with it...

    I will read some more regarding the comments above and attempt to fill my brain with more info so I can work out what is best...

    Thanks again everyone :bigsmile:

    Dave.
  7.  
    Have you considered hemp & lime to insulate your house? I'm not sure I like the idea of turning a solid stone house into a plasterboard box :sad:
  8.  
    Have I missed it or has no-one mentioned the obligation to meet Bldg Regs (0.35 for ext walls? if you are doing more than 25% of that thermal element. You may not have much of a choice.
  9.  
    Hi Nick, 62.5mm PUR laminated boards do meet the requirement, at least where you have an existing uninsulated cavity. I have usEd these on several Garage upgrades. Perhaps they are not quite on 0.35 in some circumstances [I havent done the calcs]. Maybe Building Control accept on the basis of the relaxation possibilities in Part L1B [IE technical limitations and loss of space]
    • CommentAuthorSaint
    • CommentTimeJun 18th 2008
     
    Nick,
    Under CERT the target for the utilities is reduction of carbon not to hit certain U values. However there is a slight twist to that in as much as if they use an innovative solution i.e. one that has not been used under EEC and that solution gives a better U value than 0.5W/m2K then they get an uplift in the booked amount of carbon saved. This is to encourage funding in the otherwise ignored solid wall sector.
    Lets face it to get a U value of 0.35 through a solid wall in a Victorian inner city terrace you're going to need a minimum build up of around 75mm at best even up to 100mm with common insulations
  11.  
    I don't disagree with either of you, Mike and Saint, but although solutions might require a hell of a thickness of insulation (from rather vague memory 55 or 60mm of phenolic foam + pl'bd), they are a requirement under Bldg Regs in many situations, and the allowances for waivers are relatively specific - It'll take > 15 yrs to pay back, or it is physically impossible (some cases are clear cut - where they are not, I wonder whose definition of 'impossible' applies?)

    In any case, part of me regrets the lost space and the other says, rather loudly, why should we object to a requirement to insulate well? The only issue is to do it right first time to the highest poss standard (which may be judged on pure U value, or on environmental standards.

    Nick
    • CommentAuthorJeff B
    • CommentTimeJun 21st 2008
     
    Saint - where did you learn about Aerogel becoming available as thin flexible sheets that can be applied like wallpaper? I guess this will be very expensive but it sounds like an attractive alternative to the hassle of fixing PUR boards, battens, plasterboards, then covering the plasterboards prior to decorating, a method I am still contemplating for my "skeilings" in our dormer bungalow.
    Thanks.
    Jeff B
    • CommentAuthorSaint
    • CommentTimeJun 21st 2008
     
    Jeff,
    I'm not sure if its confidential as yet but I hear it will be availabe around the end of July. I'll let you know as soon as I find out
  14.  
    "In any case, part of me regrets the lost space and the other says, rather loudly, why should we object to a requirement to insulate well?"

    Whos paying?
  15.  
    "In any case, part of me regrets the lost space and the other says, rather loudly, why should we object to a requirement to insulate well?"

    ''Whos paying?''

    The sinking fund which otherwise pays the fuel bills. Bear in mind that this arose in the context not of whether to do it or not, but of what standard to do it to. If you assume that someone has been paid for labour, then the additional cost for a better insulant becomes a relatively small proportion of the overall cost.

    Nick
    • CommentAuthorJeff B
    • CommentTimeJun 22nd 2008
     
    Saint - thanks.

    Jeff B
    • CommentAuthordwalker
    • CommentTimeJul 29th 2008
     
    Saint,

    Is this the Aerogel thin flexible sheets you mean:
    http://www.spacetherm.com/

    Sounds good, but not able to work out if its able to be applied like wallpaper!

    Anyone know?
    • CommentAuthorCWatters
    • CommentTimeJul 29th 2008 edited
     
    If we ignore the existing wall then I believe a layer of aerogel 3.7cm thick has a U-Value of 0.35

    0.013/0.35 = 0.037M

    You would need less than that but by how much depends on the existing wall.
    • CommentAuthortony
    • CommentTimeJul 29th 2008
     
    But how reasonable is a U value of 0.35? Please aim for 0.1 or 0.15 .
    • CommentAuthorSaint
    • CommentTimeJul 29th 2008
     
    Tony,

    That's fine in principle but for 0.35 on an existing solid wall you're looking at 33mm Aerogel, for 0.1 you're looking at 133mm. Work out the cost efficiency based on diminishing returns thermally and also impact on internal space yourself
  21.  
    Saint, Is it technically possible to fix such thicknesses [100mm] to existing walls? Adhesive plus special mechanical fixings?
    • CommentAuthorCWatters
    • CommentTimeJul 29th 2008
     
    The Celotex U-Value calculator says you only need add 45mm to an 18" thick stone wall to achieve 0.35.

    So Aerogel is only slightly better (33mm vs 45mm).. Is it worth the extra cost?
    • CommentAuthorSaint
    • CommentTimeJul 30th 2008
     
    CWatters,

    Equivalent thickness for Aerogel in that situation would be 27mm or thereabouts. The previous calculation was done for a 9" solid wall.
    Does the wall have to be battened out for the Celotex thermal board? Another 25mm
    You raise a good point though, how much is internal space worth?
    In a barn conversion arguable, in a city dwelling or room with restricted ceiling heights far more relevant?
    • CommentAuthorSaint
    • CommentTimeJul 30th 2008
     
    Mike,
    Proctors are the people to ask on the available thicknesses and fixings. I would guess at 100mm internally it would be battens and infill maybe as fixings through laminated thermal boards would be getting rather long?
    Externally it would be a similar system to those currently used with fibrous insulants
    • CommentAuthordwalker
    • CommentTimeOct 15th 2008
     
    I have now completed the upstairs... downstairs still to do.

    :crazy:Its now constantly 2 degrees centigrade warmer than downstairs (and sometimes 3 degrees warmer).

    What I have used is 25mm and 50mm (where space allowed) kingspan applied internally (to the external walls), this is finished off with plasterboard then the joints are smoothed with plasterboard jointing compound (easy and so much cheaper than getting a plaster to skim it - and it looks great).

    So I am getting a positive return already; the projected costs will be under £1000 (doing all work myself). I will post more detail and some photos when I have completed the work.

    But if anyone is thinking of doing the same I would say get on with it - it will save you money and provide a much cosier home.

    Dave.

    ps. To Chris Wardle, sorry but unless you are going to pay the fuel bills then there is NO CHANCE of using old out-dated methods which provide little in the way of thermal benefit; move on and enjoy the improvements technology bring instead of living in past.
    • CommentAuthorarthur
    • CommentTimeOct 15th 2008
     
    Well done dwalker.
    Please tell more about how you fixed the boards, whether you used a parge coat on the wall first for airtightness, whether you returned the insulation onto the ceilings and internal walls (as is recommended by the more cautious) and how you dealt with windows.
    Also, what put you off using greater thickness: cost, difficulty fixing it, or loss of space?
    Thanks
    • CommentAuthorJeff B
    • CommentTimeOct 16th 2008
     
    Saint - back in June you hinted that Aerogel would be becoming available in thin sheets that could be applied to walls like wallpaper. Any news on this?

    Jeff
    • CommentAuthorJeff B
    • CommentTimeOct 16th 2008
     
    dwalker - four questions please:

    Did you use a vapour barrier behind the Kingspan?
    How did you fix the Kingspan to the walls?
    How did you attach the plasterboards to the Kingspan?
    How did you decorate the plasterboards?

    Thanks.
    Jeff B.
    • CommentAuthordwalker
    • CommentTimeOct 16th 2008 edited
     
    Hi,

    I have uploaded a few photos and some text detail that should answer most of the questions.
    Please read:
    http://www.dwalker.co.uk/other/insulating-the-house/


    Thanks for your interest - now stop just reading about it and get on with it...

    Have a good busy weekend

    Dave.
    • CommentAuthorJeff B
    • CommentTimeOct 17th 2008
     
    dwalker - I've had a look at your webpage which as you say answers my questions. You are obviously not worried about the cold bridging effect of the battens?

    Jeff

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