Great_scot_selfbuild

They don’t have to be. We have a steel ring beam and columns - they have 2 coats of zinc oxide and 2 coats of bitumen. Galvanizing would have added a lot of time & many thousands £££

This is (slightly) encouraging. Do you have any photos of this by chance? Was the internal face of the steel covered or were both sides left visible/uncovered?

Yes, ordered. Frustratingly, there were many design discussions where this should have been raised by those who do it for a day job (and were being paid to…). I’m more than a little angry😡

The original design was for the column to be inside the windows, but the timber frame structural engineer stated that it ‘had’ to go in the corner. TBH this really hacked me off that they weren’t able to calculate a small cantilever for the loading. Ultimately I trusted the collection of design professionals involved in the whole build / design (and I had them all join joint design meetings). I’ve got to the point where it can’t be changed now, and in the general scheme, we can come up with a solution I expect using the Aerogel type of product. Yes, it’ll still have the steel passing through, but the internal being empty wouldn’t help. Thanks for the link to an earlier thread - I’ve only read part of it so far, but it’s already giving me confidence in finding a solution. TVM!

We have steel columns (250mm square cross-section) in the corners of our timber frame with steel lintels which allows for glass on 3 sides. The steel is visible inside & out, and although I’ve been asking for the detail for some months, only now that we’re very close to installation have I established that none of the design team (Principal Designer - architectural designer), Timber frame manufacturer (designer, structural engineer, production manager…) has mentioned it until I have pointed out that there’s no insulation in it (on the drawing). The drawing I'm concerned that there's been no design discussion about how they will be prevented from becoming a very significant thermal bridge. Cue silence… In the interest of now finding a solution rather than playing a blame game (adds no value), I’m seeking this group’s thoughts and experience. One suggestion has been to drill holes to inject expanding insulation into the column, with holes positioned in line with where the window frames will go (this method would need more than one hole to get it in far enough and fill the full height; the holes could be subsequently weld-filled afterwards, and this would obviously need approving by the structural engineer). AAAAARRRRRRRGGGGGHHH!!!! So frustrating….

Do you mean upstand above the flat roof? If so, there will be a lip of some sort for the guttering. With your warm roof, did you just take the wall insulation up to the underside of the roof board (rather than this drawing showing it stopping at the underside of the joists)?

I had wanted to go back to option B, but the flat roof and ventilation gap will be a paint to sort, so I’m thinking the option A - I think it’s just a case of taking the wall insulation up to the top. Worth adding that I only received this warm roof design earlier today (5pm) and haven’t yet had a chance to ask him this question - but it will be with him tomorrow!

It doesn’t feel like I’m getting very clear advice from our principal designer. Any comments on these options? Thanks in advance.

Which is best and why, or is there nothing in it between 11mm OSB and 12mm Medite vent panels for the roof sarking. Our roof will have 350mm of warmcel between the rafters (U=0.11), with 50mm air gap above the sarking by means of battens & purlins supporting a corrugated steel roof sheeting. The original scope of the timber frame had 11mm OSB listed but the designer has specified 12mm Medite vent and so I’m being asked which I would like. The price difference is £10/sheet, and we need 164 sheets, so £1,640 uplift for Medite vent. Have any of you used both and what would you go for and why? We’re going for quite a high spec performance build, and have prioritised the fabric of the build. If there’s a material benefit/value to be gained then we would consider this extra cost, but we can’t afford to do it just on a whim. Keen to get the experienced view from this group. Thanks in advance…

Any recommended tools / method for the UFH layout/circuit designs?

@BartW Thanks for creating this thread - having read it now, I think I’ve saved myself a lot of work being led down the comfopost path by some M&E suppliers. I’m becoming less trusting of the technical competence of some of the companies I’ve reached out to and am finding myself doing so much double-checking and calculations myself, I’m very interested in how you’ve gone about designing the UFH / ASHP / DHW system. I’ll be starting my search for tutorials and advice on how to go about this, but would welcome any advice you can offer?

@JohnMo amazingly helpful and clear - thank you!

@JohnMo sorry, not sure I follow - you’re saying the 7.5kw isn’t the best fit? They’ve used this SAP figure to give a 4.35kw requirement, and then (presumably) scaled it up to a 7.5kw HP to cover the DHW. Not that I disagree, just trying to understand - which bit of this shows that 6kW isn’t big enough at -3? And is 7.5kw big enough at -3, plus covering DHW?

They used a statement in my SAP assessor’s report that stated heating requirement as 16.7627w/m2; 260m2. (Screenshot attached)

@JohnMo @SBMS @MikeSharp01 @jack @Marvin Thanks for all your input - most helpful. After challenging/questioning the suppliers' quotes they have revised their proposed solution and Cool Energy currently is looking most favourable (MCS umbrella etc.) and has reduced the ASHP proposed down from 14kW(!) to the following: Proposed Solution: We recommend the following setup based on your requirements: Heat Pump Output: We recommend a heat pump with an output of 4.354kW. Design Temperature: -3°C ambient temperature with a 35°C water flow temperature, suitable for underfloor heating (UFH). Heat Pump Model: We recommend the Cool Energy CE-ET10, which can modulate between 3.89 kW to 7.48 kW at the above design temperature. Hot Water Cylinder Size: 250L, calculated at 50L per person plus an additional 50L. Design Temperature Explanation: The design temperature of -3°C ambient and 35°C water flow is chosen to ensure your heat pump system provides reliable heating even on colder winter days while keeping the water temperature low enough for underfloor heating efficiency. This balance helps maximise energy efficiency and comfort throughout your home. My interpretation of this is that whilst the say 'recommend an output of 4.354kW' which sounds ok to me based on my estimated heat losses of just over 3kW plus an allowance for the DHW - I'm not sure how to calculate/estimate this? and haven't searched around yet; however their model can modulate between 3.89 - 7.48kW; am I correct in assuming this would be referred to as a '7.5kW ASHP'? Just wanted to share an update and see if anyone had an opinion on this proposed ASHP solution?

@SBMS Thanks. Does that heat loss mean 3kW heat pump?! (not clear what duration it is over - I saw another post that referred to multiplying by 24, assuming it to imply it is an hourly heat loss figure, but basically I'm still unclear. Volume - I hadn't clocked that was a manual entry and I hadn't changed it. You're correct, volume is 879m3; floor area is 131m2 but tall ceilings and upstairs within the roof space. Thanks again

@JohnMo sorry - can you explain what you mean here? (Assuming DHW = Domestic Hot Water), but not sure what you mean about allowing room for it?

Ok, so please excuse the basic questions... 1. Internal wall area = is this just the external wall dimensions? could I just as easily calculate the external wall area (noting that this ignores the depth of the first floor and the thickness of walls that are perpendicular to the external wall, but as it's just a simplified calculation I assume this doesn't really matter much) 2. Internal roof area = could I just measure the roof? Ours is a warm roof and the upstairs is almost all inside the roof fault (small top collar) 3. Internal floor area = assume this is the sum of both floors? And the most basic question till last... 4. Which cell contains the figure I'm looking for as to size of my ASHP? I've read some comments about multiplying the total heat loss power by 24(!?), but couldn't see anything on the spreadsheet that mentions or suggests this. Grateful for your help in spelling out the obvious to me! (screenshot attached but sure I've not got some of these bits right; temperatures not changed from the default)

Any advice on how you identify companies offering this, and then the tricky bit, assessing whether they are any good or not?

I clearly need to bump this up my priority to read up on this in detail.

So we’re going for a very airtight performance timber frame, and visited a nearby build who built to passivehaus spec etc. This was their second self-build and one of the comments they wish they had done differently was route the hob extractor directly outside rather than use a recirculating one, as when it’s operating the noise is noticeable and an annoyance. This may be because they’re comparing it to their previous self-build which went straight outside and wasn’t noticeable inside when operating; it could be that the recirculating extractor isn’t actually that loud. However, we’re in the position where it’s not too late to decide to send the extract air directly outside. We like the idea of it running almost silently, but how do we maintain the airtightness when it’s not operating? Anyone done this? Thoughts?

@Mr Blobby this is a useful thread - did your install and setup go well? Can you share any photos of the end result (pipes through the wall for intake and exhaust in particular? Thanks

@JamesPa thanks - very helpful and clear. I’ve had the same BPC sales rep come back now saying they have checked our SAP report and they have calculated it to be 8.5kW heat loss. I need to do my own check using the spreadsheet tool from Buildhub, but I suspect it should still be lower. TBH they’ve already lost my confidence for a few reasons, but not least defending their method, then running the calcs and suddenly it’s dropped from 14kW to 8.5kW with next to no effort. Then there’s the radio-silence when I asked for clarification about which part of Approved document F he was referencing (yes, F is ventilation - not heating…). As for finding a reliable installer, I’m now taking a different approach by looking at sourcing the parts separate to finding the installer. Everyone I’ve approached so far simply seems to increase their quote/cost by £7500 so they pocket all the grant (combined with the list of tell-tale warning signs you’ve listed).

Any recommendations for suppliers of ASHP/ hot water cylinders / components?

@JamesPa I noted this input on a previous post/response of yours and I've been on the lookout for those aspects in the quotes. There are very few that have come across as honest and accurate (disappointingly). @JohnMo@JamesPa Thank you both! Great input - very much appreciated.