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What's the thinking behind the double dpm? Just to save on messing around with blinding?

That's what I am hoping, I'd be able to reduce the cost of insulation quite a bit by going without foil.

Morning, With regards to PIR insulation when placed under floor, does it matter about being foil faced? My floor will be concrete slab / DPM / 120-150mm PIR / UFH pipes / 75mm concrete screed. If the answer above is yes, is there anything I could use on top of the PIR to replicate the foil face, like an aluminium VCL like this? Thanks

Looks good, keeping the top in line with the windows was a great idea. I'm curious about the DNO notification. Was your electrician MCS certified or just a regular sparky? My install will be DIY and I don't want to have to find a MCS company to try and sign it off.

Thanks, that clears it up. Yes it is new build. Make up is to be hardcore, 150mm reinforced concrete, PIR and screed on top. So DPM below the slab and a polythene below the screed.

My floor will be made up of hardcore, 150mm concrete, PIR insulation with underfloor heating clipped and 75mm cement based screed. Just wondering what is the preferred place for the DPM? Below the main 150mm slab or on top of the slab before the insulation? Thanks

Both wagner and midsummer said that the mounts could be fixed directly to the sarking. It is a garage roof so will never be a warm roof.

Sorry I just screenshotted that from the manual to show the centre. I wasn't suggesting drilling the GSE mount. Mine are mounted on sarking as we are in Scotland, so unable to run cables under the straps/battens. I presume for me I will need to just run each set of connectors through the sarking in the centre of every mount and do the connections inside?

Has anyone used GSE in roof system? It is not clear in the manual where to pass the cables through. I presume you can just drill a hole anywhere in the centre of the mount, as this should be a dry area, and pass the cable through? Thanks

Thanks for the advice on the CU. What terminals did you use inside the box? On the subject of solar, would it be possible to stay off grid with the system I spoke about? As I would like to avoid the cost of having a MCS installer involved and there is no point as FIT wouldn't be applicable? I presume a normal sparky won't be able to sign the system off.

Thanks Dave, I didnt realise the PV diverter worked via current clamps, I had presumed it was switched from the inverter and therefore the inverter and diverter had to be closeby. That will be fine then, no extra cables needed will be a bonus. Just need some decent quotes now. I may be worth waiting till after the FIT ends, should drop the price of systems a bit. Yes that was the plan for the garage, didn't fancy trying to fit 25mm swa into the CU.

I should have given a little more info Dave. The house foundations and blockwork is in up to DPC. The power is already in and live on site with a meter and small temp CU, in the bottom right of the house where I have shown the yellow cable. The yellow cable is a large 25mm service cable that I will supply the garage with, in the same was you suggested (but in the opposite direction). The yellow cable goes to the far end of the garage, this was to save a lot of hassle as I have some thick concrete hardstanding to the front which I would rather not disturb for now. The soakaway and septic tank are also already done. Thanks, Bryan

Looking for some advice on installing solar panels. At the moment we are putting up our detatched garage, while the weather is bad, aiming to start the house kit in the new year when the weather improves. I am not required to put solar panels to obtain my SAP rating but I would quite like to, depending on costs, to work along side the planned ASHP. I was looking to install the panels on the garage roof (shown in red), this is roughly south facing (possible 10-15deg North). Currently I have a service cable (shown in yellow) run from where the meter/CU sits at the house, to the corner of the garage where the CU will be. I presume, for this to work with solar, I would need another cable back to the house, where it could then be switched between the mains and the water heater. Distance is around 50meters, would volt drop be an issue? Would it be more efficient to have the inverter in the house or garage? Thanks. solar.pdf

Not sure why there would be an issue, I built a little wooden hut, covered it in some spare timber frame membrane and put a board inside. DNO was happy to run the main cut out to it and then the supplier came yesterday and fitted isolator and smart meter. I have bought a small garage consumer unit with RCD that I will fit and a couple of IP sockets.

I had a conversation regarding this with a BCO and they said as long as the fire door has a threshold that would stop spills he would be happy (this was for a Scottish property).

It is 250m2 and yes new build. ProDave, I am not looking to make the house worse. I am looking to see if there are any tips or tricks to maximise the RHI payments. For example, looking at the figures for the heat pump that A_L provided, having a design temp of 40degrees for the system instead of 45, makes approx £700 difference to the payments. I had a look at the DIY install, but if I can get the RHI payments to be approx the same as the installation and offset the outlay with the Scottish loan scheme then it is a no brainer to pay for a Mcs install for my circumstances.

Also, does anyone know what the SPF/COP is for a NIBE F2040 ASHP? I looked it up in FSAP2012 but couldn't see a figure anywhere.

Hi guys, currently deciding on my heating options. My preliminary EPC is coming it at: Space Heating Demand = 13473 KWh/yearWater heating demand= 2612 KWh/year So 16,085kWh/year total. This brings the RHI in at £8400 over 7 year (based on a ASHP with 3.6COP). However, I could really do with getting the EPC to come it 20000 kWh/year, which would increase the payments to around £10500. Any ideas on how I could get the energy demand up without adversely affecting my SAP report?

Well if it is solid the only thing down there will be the 110mm waste pipe, so that is my concern really.

Thanks for the input. The current FIT rates put my payback at around 11-12 years on current quotes. The payback seems to be similar for a self installed system of the same size. Over the life of the system the FIT clearly wins, however does involve a large outlay at the time of building, which I would prefer to avoid.

I am currently trying to do a cost comparison between joisted floor and solid slab. I am wondering, if I was to switch and go for joisted floors, what sort of heat output difference and efficiency drop would I expect by having a say 150mm PIR/50mm biscuit mix/chipboard vs 150mm concrete/150mm PIR/70mm concrete or 50mm screed. I also have the fear about never being able to get under the house for maintenance on the solid slab too. Thanks

I am looking into my options for my heating choice and whether or not to install PV. My question is, do I need the solar PV to be installed by an MCS accredited installer for the purpose of SAP and getting my EPC? The feed in tariff is so low now I think I would be better to buy a kit and install myself and forget the FIT. For a 4kw integrated system I think it will be 3500-4000 self installed, while a MCS installed system I think will be 6000-6500. Thanks

Thanks for the replies. Yes my spec is to have UFH hence the slab. This is also the main reason behind wanting a slab instead of timber joints, as it is more simple and efficient for the UHF. I can't comment on the strip foundations. The house will be 1.75 storey. Again, unsure on why it is 140mm block instead of 100mm, I will query. The 220mm to the front is due to the site sloping away, so it will be about 600mm drop. The 150mm concrete with screed sub floor - Does this need to be ground bearing? Isnt all the load through the strip founds? Isnt the only load from the screed then onto the PIR or EPS insulation?

I have a query on my foundations and would like some opinions. We are going for a solid sub floor with strip foundations. The architect has specced the strip foundations as I expected but for the sub floor he has specced 150mm hardcore, then 150mm reinforced concerete, followed by the insulation and UFH + screed. I was not expecting the sub floor to be poured concerete, I was expecting this to be hardcore + blinding sand followed my insulation and screed. The extra concrete is 3-4k worth extra cost, is this normal practice? I dont see why as it is not load bearing, the strip founds are taking the load. I have attached the spec and foundation plan.

JSHarris, thanks. I will have a good read through tomorrow. Thanks for the points on the frametherm. Certainly is a lot of work installing the PIR if cutting. Just had a quick google of the wood fibre and it seems pretty expensive, in the region of 10p/m. Does that sound about right? Also I presume that would need to be decided early on to allow the frame to be spaced in a bit from the blockwork?