Iceverge

Its one of my regrets,not stick building on site. Taking a bundle of timber and ending up with a house is special. I had a look at some wall buildups last night, in terms of cost only for a project in the back of my mind. The most economical way to build for my target u value of 0.15 was externally osb sheathed 200*44s, AT membrane, a 44mm service cavity. pumped cellulose and rockwool respectivly, 15mm plasterboard, soundboard if you're feeling generous. I like the idea of a continuous insulation layer outside then studs. Great for thermal bridging. The issue with external foam is the ludicrous price of the PIR, and the amount required to bring the dewpoint outside the sheathing. (probably a non issue with good airtight treatment taping of the OSB to be fair) Also pir shrinks, underperforms in cold weather and burns in a nasty manor. In fact if it wasn't for the headline K value (remember laboratory conditions only) and the sometimes unbelievable marketing I don't think anyone would bother. Don't forget the cost of screws too. At 30-40p each long screws can add up quicky. If I was building again I'd use the method I described here. Better still it can all be put together with a nail gun.

Airtightness, complexity of design. Insulation levels. The occupants value on air quality and comfortable . £1500 sounds like a bargain, was that from a supplier? Theres a good few threads here where this has been debated to the nth degree. In short no it will probably never pay itself back in cost terms. Then there are lots of things in our house that certainly have no payback. Footpaths, paint on the walls, skirting boards, windows, internal doors. Floor tiles, carpets, fitted kitchen, tumble drier. 2 of the 3 toilets, most of the furniture. Wife, children, etc etc etc. You must decide where the accountant on your shoulder gets told to bugger off!

It depends. Yes. £3-9k.

It might not be much price difference to just put in a pvc door/window.

I assume your home idea of home entertainment is sitting around watching a 2 bar fire 🤣.

Welcome welcome. Spend £150 ish and buy a copy of PHPP. With an engineering brain it's actually quite possible you'll enjoy it. Looking at the numbers (which are all just school level physics) brings amazing clarity to design in an industry that is rife with misconceptions.

Excellent, I didn't know this. I never liked the idea of a flat sheet of metal on a flat sheet of OSB. Far to much chance of moisture between the layers not being able to dry out quickly. The closely spaced battens is a far most robust idea. 10/10.

I'm assuming that the wall between you and your neighbours is a solid 225mm block/brick wall? If so the acoustic plasterboard won't make much difference as you already have lots of mass there. More important for noise is ensuring all air pathways are sealed 100% and then decoupling the walls to prevent any transmission of noise through the structure, think a stand off stud/resilient bars. ( You shouldn't need to do this if it's a cavity wall) Once the noise is catered for, and you really really really need the room space insulated plasterboard is probably the goto, dot and dab or mechanical fixed. It is silly expensive mind you for the thinnest stuff.

A basement might be an option depending on the ground conditions. I don't think they're as expensive as folk imagine.

Crikey, it's a matter of determining how long a piece of string is... Broadly, the larger the floor area the more floors it justifies. At a guess, from viewing developers catalogues for one off houses with prices, < 120m2 for a single story, 120-240m2 for 2 story etc etc. Obviously if you get a superb price for foundations and roofing it sways the deal.

Can you supply a cross section of your roof for clarity please? A sketch will do.

Given that buildings heat demand varies so greatly it would be perhaps a little meaningless to draw and any specifics about an ASHP ( or any other CH system) even if you had a good return of surveys. Perhaps the question you might have hoped to ask was what was the real world COP of ASHP with regard to space heating and DHW. Perhaps the variables could be . 1. Annual, monthly, daily building heat demand + DHW. 2. Annual, monthly, daily breakdown of an ASHPs acutal kWh usage. 3. Annual monthly, daily breakdown of external temperatue + humidiy. 4. Flow temp of central heating and Temp of DHW. 5. Size of ASHP vs peak heat demand. This data would be very handy to arrive at some optimum design and setup's of an ASHP. Unfortunatly the level of survilance required would be impractical without a huge sample size considering the variations in heating and DHW and heating preferences , even within similar houses. In general however for the best COP...............(corrections welcome of course) 1.Size the ASHP suitably so that its not too large and constantly cycles on and off. ( a buffer may help) 2.Is big enought that it can run without defrosting 3.Couple it to as low temp a CH demand system as possible (UFH in a thick slab) 4.Heat a large volume of DHW to as low a temp as possible. ( better than less water to a high temp) 5. Site the outdoor unit in an area where it will not struggle for airflow. 6. Use sensible large diameter pipes excellently insulated with as short a distance as possible to bring heat inside. It would be nice to have real world data to help optimise for purchase cost vs performance rater than rules of thumb I agree.

I have to agree with @Jenkientirely. Keep it simple and keep it square. When we started we thought it was a case of €/m2 regardless of design. 3 planning permissions later we ended up with a completely rectangular box. No external porches or add ons. Design 2 was a stepped tetris block shape. Changing to the final rectangular floorprint saved €30k with no loss of floor area. Were the council specific on lightly approval for ridge height? Do you have a maximum plot width that you can use? The design can be made more interesting with verandas, conservatories, overhangs, uninsulated porches etc all outside the main thermal envelope. The designs you have picked out are not hugely complex or expensive to build to bog standard levels of detailing etc. However given the oppurtunity you should aim for excellent levels of airtightness and insulation. With a simple design these will be achievable with no extra cost. Our house ended up cheaper than an equivilant bregs house with an ASHP as the passive house detailing meant we could omit a conventional central heating system. It's an erie feeling walking into a house and feeling the warmth with no central heating on. Once you've done it it becomes very difficult to see why everyone doesn't, espically as it can be done on a tight budget.

Have you considered blown in cellulose?

Cellulose can be blown in on site. Better than plastic insulation too IMO.

How about mounting the Oil heated cylinder above the ASHP but plumbing in parallel. Would this not allow the upper cylinder to be heated by convection to 40 deg but prevent the lower one being heated by oil.

edited as posted in wrong topic.

Have you considered using your concrete slab as a Battery? If my calcs are correct, with no losses, an extra 1.5m3 of concrete holds 1kWh/degree. Adding 75mm of concrete to your slab of say 100m3 will add 5kWh of energy storage per degree of temp you raise it. If you raise the temp of the slab by 3 deg overnight its a 15kWh battery for an extra ~£700 in cost. Similarly an extra DHW tank at 300l can store 7kWh per 20 degrees. We use an immersion to store 14kWh overnight, again at a cost of about £700. The same ~ 30Kwh of Battery storage would cost over £10,000.

Watching with interest here as I was contemplating doing the same with an all in one ESHP. The payback is questionable at the moment but if we could heat ~600l of water to the low-mid 40's by putting it in series/parallel with the existing UVC, the bounce in COP might make it a runner.

Most timber frame factory builds are used by developers who can squeeze the TF companies, also they have many repeated designs on large sites vastly reducing the cost of crane hire, design and erection teams. Mass produces TFs are sadly almost all built to just tick the Bregs minimums. Us self builders are somewhat more forward thinking. The gap really narrows once you go to one off designs and builds. Having scouted a couple of bog standard TF factory builds the general care and attention to continuity of insulation and airtightness+windtightness membranes was poor. If you wanted to spec to a passive level stick building was competitive with the few excellent TF companies that provide this . This cost difference will no doubt change when passive goes mainstream no doubt.

Sand cement wet plaster here followed by skim. 0.31 Ach 50. Many hours of prep with airtight paint and tape beforhand however.

Actually I've underestimated it. This is the result for 63mm studs. If you want to minimize wall thickness omit the 45mm service cavity and include a 22mm strapping instead.

I wouldn't bend over backwards with thermal conductivity values. The actual quality of install is more important. To get PIR exactly correct is very tricky. It's only performs to its stated K value under lab conditions. Also it's very expensive compared to mineral wool and EPS. I would get the the existing mineral wool vacuumed out of the walls. Then blow in EPS beads. Put an airtight membrane inside your framing, seal it to all windows and the floor and ceiling. Blow EPS beads behind. Insulate the service cavity with mineral wool. Then plasterboard. Over all U value of about 0.25 at a guess. It would lightly perform much closer to this rather that PIR between studs.