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Hopefully you do not have a dew point in your timber frame! Dewpoint is 100%relative humidity and water condenses from the gas phase to a liquid on any solid material whose temperature is less than the dewpoint temperature. It can be acceptable for a dewpoint to occur in the exterior layer of a wall buildup if that layer is unaffected by liquid water and it cannot spread to water sensitive layers (e.g. masonry façade of a cavity wall)

No, there is a danger that the insulation will undergo hydrolysis (breakdown to its constituent chemicals) in permanently damp/wet conditions. http://blog.celotex.co.uk/technical/what-celotex-insulation-can-be-used-in-floor-applications/

What you need is to compare costs for the same thermal resistance (R-unit) of a standard area of material. I.E. Cos.t of 1 R-unit per m2 (£/R.m2) e.g. 100mm RWA45 can be obtained for about £13 ex vat (2.88m2 ), has a thermal conductivity of 0.035 and thus for 100mm R=2.86. Therefore it has a cost of £13/2.86*2.88 or £1.58 per R unit per m2 ?

Assuming loft heated as rest. <5kW at 'passive' specification. 8 to 10kW at current building regs.

Any explanation for the relatively poor 3ach? Can it not be upgraded? It would be your most rewarding upgrade. Edit:- Assuming MVHR in both cases then reducing from 3ach to 0.6ach looks like about a 35% saving on total heating bill

@MikeGrahamT21PVGIS for Leeds in February gives about 30kWh/month for 1kWp on East and West 35° slopes and 50kWh/month for South 35° slopes. So I do not think anything is seriously wrong. I would expect the outperformance to be proportionately higher on sunny days and less on cloudy ones.

@vfrdave, not unless there is a high thermal conductivity pathway (i.e. masonry) from the floor slab through the area insulation to a stub wall/footing

Only because of the design of current thermal stores. See tank B in attached pdf. A store charged to 60°C provides close to 120% of its volume at 43°C TZS_10.pdf

how about this then http://www.caravan-components.co.uk/Caravan-Sealant-Mastic-IDL99-Cream-in-400ml-Tube

AC50 12 for £22.90 inc vat https://www.sealantsandtoolsdirect.co.uk/silicones_and_sealants/intumescent_fire_and_acoustic_sealants/everbuild_everflex_ac50_acoustic_sealant_adhesive_c4_380ml_box_12_P23506.html

Sorry, do not really understand this, I have given heatloss for 20°C inside 0°C outside. If you want greater capability then heating to 20°C when -10°C outside then add 50% to heating load. An oil filed radiator with timer and thermostat, about £40 from Lidl/Aldi will achieve this, even if only interim solution. An aircon unit (air to air heat pump) maybe £500 - £1000 will solve this. They can even be DIY'ed (just an example, heating output about 1.7kW) http://www.cooleasy.co.uk/categories/diy-air-conditioning/unico-air/unico-air-8-hp.html I can confirm that a professional install would be in this ballpark (at least) If this is anything like accurate then you need to look at low power alternatives.

Look at it from a heatloss point of view. Assuming an outside/inside differential of 20°C then with 150mm of PIR or equivalent on all six surfaces the heat loss is about 340watts, plus say 180watts for 6m2 glazing, ventilation of 0.5ach with no heat recovery is about 200watts. So about 720watts, then subtract input from solar/bodyheat/appliances. Do you really need a GSHP?

Unfortunately the amount of heat stored in any fixed volume of air is too small for this to work. ASHPs process several hundred cubic metres of air per hour to obtain their energy and one/two passes would almost certainly reduce the temperature to no higher than the outside. After this it would be colder than ambient air.

The manufacturer says Majcoat can be exposed for upto 8 weeks while Majcoat 150 can only be exposed for upto 4 weeks.........so https://www.siga.swiss/global_en/catalog/majcoat

Not sure I would be happy using OSB/OSB2 for sarking. https://www.norbord.co.uk/media/1297/sterlingosb-brochure-24pp-2015.pdf pages 5 &7 http://wpif.org.uk/uploads/PanelGuide/PanelGuide_2014_sect2-6.pdf page 1

from section 6 of BBA cert, '1.24 m2·K·W–1 R value for SuperFoil SF19 (41.9 mm thick) with no air gaps either side ' wiith air gaps the thermal resistance will vary with orientation, as suggested here https://www.roofingsuperstore.co.uk/product/superfoil-sf19-multi-layer-foil-insulation-15m-x-10m-roll-15m2-1.html?gclid=EAIaIQobChMIs5GD97OR4AIV6Z3tCh16IQxeEAQYAyABEgJHufD_BwE although I do not know where the R values come from

Here is the BBA Cert for the product. According to this the SF19 variant is 42mm thick and has the insulating effect of about 55mm of ordinary loft roll. It is also to be considered a VCL with a vapour resistance of 1200Mn.s.g (Polythene is normally about 300 IIRC) Superfoil BBA Agrement Certificates Roof and Wall.pdf

@willbish , 15/5°C is the CIBSE defaults for this calculation. I am not entirely sure why they have a positive condensation rate at the interface in layer 2. The vapour pressure is lower than the saturation vapour pressure and the structural temperature higher than the dew-point temperature. Certainly my own CRA software (operating to the same BS5250 standard) does not indicate a problem, even with chipboard added and a 20/-5°C temperature scenario.

no, unless there is a layer more vapour resistant than the insulation on its cold side, good ventilation on the cold side would reinforce this. What is the thermal conductance and vapour resistance of the insulation? a (non-tenting) water vapour permeable membrane at this point is really there to act as a backup should the final layer (i.e. slates etc.) have a fault and let water through

Assuming your inverter has 2 MPPT trackers (usually is these days) and the open circuit voltage of both strings are within the MPPT voltage range of the inverter then no. There might be a slightly lower part load efficiency of the tracker with the smaller string but it should be greatly outweighed by the increased production.

In as much as the current floor is probably at 15°C or less and a UFH floor in this house might be at 25°C or more and would half the floor/barefoot dT, then yes. But the high thermal conductivity of concrete will mean there will always be some cooling effect.

Assuming a 8m x4m floor slab it currently has a U-value = 0.89. Vertical edge insulation (EPS lambda 0.036 W/m.K), down the inside or outside of a foundation wall gives depth/U=values 0.5m/0.62, 0.75m/0.55 and 1.0m/0.50. thicker/deeper insulation has relatively little additional effect. A 100mm of PIR with no edge insulation would give a U-value = 0.18 At the the moment the cold floor effect can only be mitigated by using a floor covering with a low thermal conductivity as you have a massive thermal cold store in the floor..

Perhaps @ProDave can confirm the maximum thermal conductivity (lambda) of for wiring purposes of an 'insulator'. I think it is 0.04W/m.k, so anything higher than this would not require derating.

Input (or Charge) - Allows electricity to flow into the radiator until a temperature corresponding to selected setting is reached. 1. - LOW Temp........6. HIGH Temp Output (or Boost) - Opens a damper when store falls below temperature corresponding to setting. 1. – HIGH temp....... 6. – LOW temp Assuming E7 type tariff and simple storage radiators. You must alter the input control to import the correct amount of heat for to-morrow’s weather. Weekly or seasonal changes are usually adequate, with it set to 1-2 in Sept/Oct & April/May and 5-6 in Jan/Feb. The output Damper (usually a metal flap that you can see through the output grill) is designed to close at the start of a charge period – but do not depend on it – the output control should be turned down to the minimum value before going to bed. In the morning the radiator will be giving out heat in an uncontrolled manner – leave the output control minimised until heat required – turn till damper opening is heard/visible when required to release extra heat . Alternatively the output control can be used as a crude timer – low numerical values open relatively early when contents relatively hot, high numerical values open relatively late when contents relatively cool. N.B. The opening time for any given output setting will vary for different input settings. (As the time taken for the contents to fall to a given temperature will vary with the temperature set by the Input control)

1) The SAP report means little/nothing to the average home buyer. 2) The average homebuyer does not know it exists until it is (hopefully) presented to them when they purchase the house. 3) For the actual SAP score there is no minimum standard (except when renting). The SAP score is actually a cost index which has zero energy cost at 100. It is very difficult for a mass produced house to get better than a 'B' rating, so I think mass builders do not push it because usually normally who wants a B rated product?