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A_L last won the day on October 12 2017

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  1. A_L

    do it yourself Insulation

    Based on the claimed performance it is as good as the same thickness as PIR board. It is however on a 'cost for equal insulation performance' three times the price of PIR and six times the price of Rockwool RWA45 batts.
  2. A_L

    do it yourself Insulation

    Not really, with thermal bridging of the timber fraction a reasonable build-up gives U=0.16. Not so low compared to people here.
  3. A_L

    do it yourself Insulation

    Only closed cell polyurethane foam comes close to PIR, I do not know of any DIYable kits using this. All the kits seem to be open cell of one sort or another and are only about as effective as Rockwool batts.
  4. A_L

    do it yourself Insulation

    For the same insulating effect pretty much anything will be thicker, cellulose would have been 0.04/0.023 or 1.74 times as thick (or about 350mm). Rockwool batts, (RWA45/RW3) the basic type not the mineral wool/fibreglass batts sold specifically for TF are economical effective and DIYable. They would be about 300mm on the same basis
  5. @Andrew for the specific example in central England the saving is around 0.78kWh/m2/yr
  6. A_L

    Loft insualtion

    Cold external air entering the loft/attic will displace relatively warm air between the two layers of insulation making the rafter layer ineffective. The loft as originally designed must be air tight. No ventilators, particularly in the soffit, no day light visible from inside the loft, particularly at gutter level.
  7. A_L

    Loft insualtion

    Only if no air enters the loft from outside.
  8. Actually isn't it the evaporator that freezes? 😉
  9. A_L

    Electric cables, conduit and eps

    Given that polystyrene reacts with PVC insulated cable, on a safety first basis I would avoid having PVC conduit in contact with EPS. There will be the issue of de-rating the cable because of restricted heat-loss but I will leave that to the electricians.
  10. No, Bregs are m3/m2.hr and Passsivhaus ACH. Both at 50Pa over/under pressure. At low levels the numbers can be arithmetically similar, e.g. 0.6ACH corresponds to 0.48m3/m2.hr for a simple bungalow of 117m2 I have details for. Also the actual infiltration rate of the unpressurised house is about 1/20th the test number.
  11. The reason is that the thickness of one of the layers, the soil, varies across the area of the floor. The heatloss path is floor surface - soil - external air. Therefore at the edge of the slab there is little/no soil and the local R value is approximately the higher one. The area at the middle of the floor has the thermal resistance of a considerable thickness of soil and thus a higher R-value. The 0.14 U value is the weighted average of the whole floor. If you try using floors of the same area but different P/A ratios you will see the effect, since higher P/A ratios imply less 'square' shape which have greater exposed perimeters for a given area, e.g. the common perimeter of two adjoining semi's would not be included.
  12. hello and welcome, Do not put celotex on the cold side of the existing mineral wool insulation, it has a relatively high vapour resistance and particularly if it has a foil face is liable to cause the interstitial condensation you refer to later. For any given thickness Celotex will have about 2x the insulating effect of wood fibre board and both will be relatively expensive compared to mineral/fibreglass wool rolls. 200mm of loft roll wood give the desired effect without the expense of sheep's, wool. If you are using a membrane to reduce 'wind washing' it must be vapour permeable to prevent condensation. Putting above two 100mm layers and below one layer puts out of the way while still having the desired effect. It need not be 'airtight; windtight is sufficient, e.g. Tyvek Housewrap or equivalent. Loft boards will reduce heatloss but the extent will be dependent on the insulation backing. Do not use Celotex or Steico across the joists unprotected, the compressive forces from standing on it are to high. Reasonable storage with board on top would be O.K. Your first insulating task is to fit bonded bead CWI, try the Energy Saving Trust for local subsidised offers.
  13. A_L

    Remote island crofter

    Hello and welcome, Boreholes are costly, I assume you are thinking of them because of rocky/thin soil? Also the contractors probably will be reluctant to quote for your location, further increasing price. Here is the blog of someone who has built a low energy house with renewables on a 'remote island' (Raasay). https://lifeattheendoftheroad.wordpress.com/
  14. A_L

    Ventilation and Scottish slated roof

    @AliG , air tightness moisture/vapour resistance are two separate phenomena. It is perfectly possible to have an airthight membrane which has a very low vapour resistance and does not significantly inhibit water vapour movement through it. The process is called diffusion and is different from bulk air movement.
  15. A_L

    Rockwool EWI ?

    Just to double-check. The extra insulation is on the cold (out)side of the vapour membrane?