Norbert

Let me explain why it seems right to be focusing on payback period right now wrt wall U values. I have a choice to make .14 or for £6k more .11. Some of the remarks above, while obviously correct, do not help me decide. Let's just say I decide to go ahead with U .11, while my identical brother decides to build an identical house next door, but with just one exception, he uses .14. Some time later both houses are finished. ASHP, UFH, MVHR, air tightness, windows, all other insulation, .... all identical. We are both very pleased with our comfortable houses. How can we, or anyone else tell the difference? It seems to me that the only difference is that I am spending ca. £50 per annum less on electricity, and he paid £6K less on his build. Thus it seems perfectly reasonable to focus on payback in this instance as there is no other difference. Or am I missing something?

So it seems like that while I had some gross assumptions as a basis for my calculations, they were correct. This begs the question why would anyone go for an additional expenditure that had a 120 year payback? I was thinking that I must be an order of magnitude out somehow. 12 year payback fine, 120 year pay back, well that seems barking mad. I intend to have a largish PV area on the roof, plus battery storage, so some of my heat pump input will be 'free', which will further push out the payback period. I have already completed Mr Harris’s spreadsheet for my design and used it to try various U values. This showed me that window and door loss, even with triple glazing, was similar to wall loss, both at ca. 30% of the total. Changing the U value from 1.4 to 1.1 did not make a huge difference. That is why I homed in on wall loss calcs to try to understand things better. The spreadsheet does not give the option to put in air tightness values, but based on comments above I understand that this becomes more important as other factors are improved. At the moment I am thinking that the sweet spot for me is U 1.4/1.5 for walls and roof, triple glazing U 0.79, good airtightness, PV and battery, quality MVHR, smallish ASHP to UFH. Seem reasonable?

I have a number of quotes from TF manufacturers. Taking just 2 of these I can have a U 1.4 wall build-up, or for an additional £6k U 1.1. I am trying to work out if it is worth paying the extra? Please check my assumptions and calcs. My answer must be wrong Ignoring all other sources of heat loss, floor, roof, windows and doors, MVHR ventilation, air tightness etc. and homing in on heat loss through the walls my calculation is based on the following. Average temp difference internal to external over a year = 10C Area of walls = 220 sq/mtrs Energy loss = wall area x temp difference x U, so : U 0.11 = 242 W U 0.14 = 308 W Over a year it would be the above x 24 x 365 to give annual heat loss through the walls in kWh U 0.11 = 2120 kWh U 0.14 = 2698 kWh If my heat pump had a SCOP of say 3.5, then electricity used to generate this heat would be : U 0.11 = 606 kWh U 0.14 = 771 kWh If the cost of electricity was £0.30 per kWh then annual cost of energy lost through the walls would be : U 0.11 = £182 U 0.14 = £231 Annual difference £50. Pay back period 6000/50 = 120 years. As I say, that must be wrong. Where is my error?

Great, found it, this is exactly what I wanted.

Our planning application has been filed. Thus I know the exact dimensions of the thermal envelope, plus all windows and doors. I have quotes from two timber frame manufacturers with options for various U values and target airtightness. I have typical U values for triple glazed windows. The house may or may not be to Passivhouse standard, we have yet to decide. However we will not go down the certification route. What I need now is a first cut estimate of the energy demand of the house once completed. Right now I have no idea what the difference would be of a TF of U value 1.4, vs. say U 1.1 ? Is it worth paying the extra?. What would the pay back period be? What size HP would be needed. Do I need A2W and UFH, or would A2A be better ?? To get to grips with this I feel I need to get a spreadsheet together with all the calcs in so I can play around with the numbers. To save me the effort of starting with a blank spreadsheet, does anyone know of a template and guidance to put something together? I guess at some point I will need a professional SAP calc done, but I would like to progress a DIY approach for now.

Are you sure it is not set to holiday mode? If it thinks you are away it would not come on. If not and room temp is below set temp for the time period then you should either see a flame icon, or a frost icon (snow flake in a house), toggle between these two with the tick

Our property is attached to a neighbouring property. There is a thick stone wall between, the wall belongs to the neighbour, the boundary is the face of the wall, their property is one floor higher than ours. We have put in for planning permission to demolish and rebuild as a detached property with a 1.5mtr gap between the houses. The neighbour has been fully consulted and has raised no objection to the plans. However he is concerned about his right of access for maintanance purposes to his gable wall in the future. My view was that he already has a right to maintain his gable wall under the party wall act. After demolition his wall still forms the boundary, it would still be a party wall, so his right of access to our property to maintain his wall would remain without a need to do anything else. Is this true? If not then I can see his point, so we would need to set up some kind of formal access agreement between the 2 properties that would persist beyond change of ownership. Any views?

We are planning a ultra insulated air tight house with UFH, ASHP, MVHR blah de blah..... However I see an issue looming, how do we keep the bedooms cold enough? We have always had bedroom windows open all winter with no heating in the bedroom, it is just the way we like it, it seems healther and we sleep better. Bedroom temp of say 15/16C seems ideal, while all other rooms are nice at say 20/21C. Given that the bedrooms would be inside the super insulated efficient thermal envelope, and the MVHR would be purring away it seems to me likely that the bedroom temp will be around 19/20C. Indeed I was speaking to someone recently who had recently moved into a new house and the biggest problem thay had was keeping the bedroom cool enough, while all other rooms were warm enough. So I was thinking ..... maybe not have an MVHR plenum in one of the bedrooms, no gap under the door, trickle vent on the window, plus opening window with NE aspect so minimal thermal gain, insulated internal walls etc. So just a partial MVHR? There will be 2 double bedrooms so the other could have UFH, MVHR etc. and we could use that in very cold weather or when we get older and want it warmer. Does anyone else have this issue and how do you solve it?

Here is a question for all you lucky lot who have completed you projects. At what stage can you move into a new build? I am thinking that as soon as the electrics and plumbing are (mainly) in and there is a working kitchen and bathroom then we would be perfectly happy to rough it for a while while and move in. However I bet it is not as simple as that. What legal requirements and inspections need to be passed? Perhaps all fire regs met, so all plaster board in place etc. The house will have 1 bedroom, bathroom, and open plan kitchen/lounge on one floor, so everything we would need. So could we move in when all that is done then continue working to complete the upstairs?

Thanks. That seems like a consistent story then. I will have 2 floors constructed using metal webs, the lower being insulated and the thermal envelope between basement and first floor, so much the same as the roof. The middle floor is entirely within the thermal envelope, so indeed that makes no difference. n.b. everything 2 meters above current ground level to get above highest possible flood levels.

This seems like a bad idea due to the thermal bridging that a lot of metal would introduce. However I note that MBC use metal web rafters in their Passive roof constructions and claim U value of 0.10, so there would appear not to be an issue. My proposed build also uses a suspend timber floor as part of the thermal envelope, so I guess the same construction would be good here too. However it just feels wrong and my instinct tells me that I beams would be better. Any views anyone?

As long as the simple shape is big enough, then that is my favoured option.

Not sure about the buffer, I will leave that to whoever specs the ASHP and UFH. I gather it is useful to prevent short cycling of the ASHP therefore more efficient. As to the positioning, yes zoning would be good. I was just trying to get an idea about how much total space is needed.

The plant room is central, kitchen on one side, bathroom on the other. So In think we already have already minimised HW delivery times. It could indeed go in the bathroom, but that would mean extra delivery time to the kitchen.

How big does a plant room need to be to comfortably contain a full suite of technology e.g. HW and buffer cylinder, MVHR, UFH manifold, battery, elec distribution etc... Attached are 2 layouts, one with a L extension, and one without. The L section takes room from a pantry/larder, which I would like to be bigger. So would the basic 4M x 1.6M be big enough without the extension? I have dotted a few plant items around at I hope realistic sizes to try to judge. In addition to the plant there would also be sink and washing machine. I am thinking no window necessary to make more room. Any advice fom anyone with a fine plant room would be appreciated. Plant & Utility-1.pdf

I am planning a gabel end section on our planned TF build to be stone clade in the traditional Lake District fashion. Apart from a stone plinth everything else will be render board and render. I always saw this as a thicker wall section with a block backing wall, then stone cladding, so a much thicker build up than the rest of the house. with wide external window reveals. The architect has suggested SureCav. Having looked at this product I can see the advantages, however intuitively I react against a single skin stone wall of up to 6.5 meters. I question iit's stability. Yes I know it is tied back to the TF, but you know .... Has anyone any experience of this product in a similar situation?

This implies to me that you think a better solution is render board and render. Is that correct?

We are in the early stages of a project that will demolish and then rebuild 2 meters higher, as already discussed in this thread: https://forum.buildhub.org.uk/topic/33630-demolition-and-rebuild-my-initial-thoughts-your-comments-welcome/ We have engaged some local architects and we will soon have completed Stage 2 i.e. we will have the concept design. i.e. basic layout, footprint, interior room layout, windows, roof config etc. This will be a timber frame house built on a block wall base. What I need some advice and info on is how to manage the role of the architects and the TF manufacturer during the design process. According to the schedule the next stages are Stage 3 – Developed Design then Stage 4A – Technical Design. At what stage should we start talking to TF manufacturers, my sense is earlier rather than later. Should I be sending them the concept design for initial comments and perhaps outline costings? With a traditional design I understand that the architects would do all the design work ready to hand over to a builder. However with a TF project obviously a large chunk of the detailed design would have to be done by the TF manufacturer. If I pay the architects to do Stage 3 –Developed Design then Stage 4A – Technical Design, am I not duplicating effort, or at least payment for services? How important is it that the TF company and architects work closely together? (very I would guess) At what point in the process is it wise to select the TF company? Based on 2 visits to local TF manufacturers it was very clear that their methods of construction would be very different. One using floor and roof cassettes, plus SIPS, the other just SIPS and constructing floors and roofs in-situ.This seems like a profound difference so no point in doing any detailed design until TF manufacturer selected it seems. Any advice from anyone who has been through this process recently would be much appreciated Edit : Just spotted this closely related thread :

If anyone else is interested I have found these : https://www.lightwaydaylight.co.uk/products/blue-performance/ It says "Thanks to two types of Blue Performance, Lightway has become a definite standard in Germany for delivering sunlight to passive houses. Lightway sun tunnels have thus become the only ones in the world meeting standards for heat loss in passive and low-energy homes." These appear to have double or triple glazed argon filled window installed in the roof insulation layer, so very low thermal bridging. Looks good!

I like the idea of a light tunnel into an internal upstairs corridor. I know it will work OK providing light, but if everything else is insulated and 3G to passiv house standards it seems like it could perhaps be the biggest thermal bridge in the house. Also could inturupt the run of PV on the roof. Perhaps movement controlled LED lighting would be better and more efficient. Has anyone else considered or had experience of this issue? Can you get helium filled 3G light tunnels?

Thanks for the input everyone. It has certainly caused me to reconsider my options. However having done that I come to the conclusion that my only options for practical, aesthetic and planning reason is to do nothing, or demolish and rebuild on the same footprint. While the site is large half of it is lower and closer to the river, so forget that. Other parts are higher but closer to the road, noisier and aesthetically horrible. In a dense urban setting splitting the the plot, building a new house and keeping/selling the old might be an option, but in a National Park planning would be difficult/impossible. If I built alongside somehow and demolished the old house then my garden would feature a huge concrete slab. Breaking that up, removing it and landscaping may be possible but at a great expense no doubt. While moving out for 6/9/12? months is a PITA, any other plan severely compromises the quality of the final result IMHP.

Bat survey already scheduled for August. Had a new roof on 12 years ago, we did have bats so had to do it in the winter as it was a summer roost. Bat slates were put in so expecting a positive. However starting demolotion in winter/early spring fits OK, and happy to incorporate new bat accommodation in the build.

This is my current thinking too. If I was to put a heat exchanger in the river there would be no abstraction, however EA apparently likely to kick up about potential leaks of whatever fluid was going round in my system. Plus if it was a well insulated house what would be the pay back period for the extra cost of ground works and GSHP vs ASHP with lower efficiency. Given that I am past 70 not sure I will live long enough to benefit.

So if I demolish and rebuild on the same footprint 2 meters higher what do you suggest that I do with the volume (footprint area x 2 mtrs) that will inevitably be created?