How much more might an air tight new build cost than a leaky new build?

[Tony L]

4 hours ago, Crofter said:

On my very simple build it really didn't add any cost at all,

 This is all very reassuring.  Thank you, & good luck with your recently announced next project.  I'm looking forward to reading about it.

[Tony L]

20 hours ago, TerryE said:

all of our wardrobe space is in built-ins / walk-ins, so no VAT

All ours will be built in as well.  I think I read that to reclaim the VAT you’ve got to be able to see the wall finish in the back of the built in wardrobe (I don’t have a problem with that) & you’re only allowed one shelf – is that right?  Is this shelf rule enforced?  I can’t see how it would be.

[Tony L]

20 hours ago, TerryE said:

When you say "I'm building"...

That's a good question.  I ask myself often, & I keep getting different answers.

 

I did the designs (several of them) & drawings to achieve planning permission; somebody else helped me out by adding a few notes. I'd not have bothered hiring them if I'd realised how easy this would have been, but this happened before I'd discovered Build Hub.

 

I think I could (with lots of help from BH) have a go at doing the building reg.s /construction drawings & heat loss calcs, if I had fewer commitments & I wasn't in so much of a hurry, but I'm keen to pay to get this done well & done quickly.  This is the next task.  Then QS.  Then we'll likely have to make some revisions to the drawings (for budgetary reasons) before they go in for approval.

 

I reckon I can make a garage base (I've done this twice before) & stick build a garage (not done before) & deal with the roof. I want the garage to go up before we start ordering the insulation, so we can store it out of the weather.

 

Due to other commitments/ time constraints & my ineptitude, others will be doing most of the building work.  I expect I will decide my partner & I will PM this between us, to save money.  I'd love to PM if it wasn't for my other commitments, but as things are, I know I won't love the experience.  I'm not yet sure whether we'll hire every individual trade, or whether we'll employ a building firm to do the next stage (superstructure without roofing finishes) then the standing seam roof (if we can afford it) & flat roof finishes, then windows, & so on.  Of course, PMing myself may not save anything at all - it depends on how many serious mistakes I make.

 

In my day job (90% desk based), I'm good with attention to detail & completing tedious tasks, then checking my own work, so I expect these are transferable skills that can be usefully deployed on my building site.  I envisage doing jobs such as preparing my B&B base, laying membrane then PIR, the next membrane, UFH pipes & getting ready for the screed, perhaps installing MVHR ducting into the metal web joists, soundproofing between floors, soundproofing & boarding stud walls, constantly reminding everybody about my precious air tight envelope, reprimanding anyone who damages the air tight envelope, sacking repeat offenders, making a DIY air suction rig & finding some leaks.  The task I'm most looking forward to taking on is the exterior cladding on the three dormers.

 

[Tony L]

21 hours ago, TerryE said:

8 years later, and we live in a pretty maintenance free house with pretty much no post move in problems or things needing fixing.  We have a high quality house and saved a lot on our build costs by doing a lot of the attention-to-detail stuff ourselves.

Well done, & thanks for sharing - this is inspiring.

[Tony L]

21 hours ago, TerryE said:

Why so much glass?  It costs a lot more than TF/blockwork and dumps heat like crazy.  I know that it can occasionally help you connect to a stunning view, but if you are overlooking the street or neighbours, then do you really want to connect to them or have them looking into you private space?

 

I’d prefer less glass.  The purpose of the glass is, to please my partner, who wants lots of glass, especially on the façade.  It’s half her money, so I’m compromising.  I’ve deleted a lot of the glass from our original approved plan, having learnt so much here on BH over the past year.  Windows have been deleted from the sides & the south facing rear elevation.  I also persuaded her that her log burner was a daft idea for this kind of house, & the chimney has been deleted as well.

 

I’m more concerned about unwelcome solar gain in the summer months, on the east & south elevations, than I am about having to turn the heating up.

 

The glass in the sloping roof above the hall/landing could be reduced, but this is helping to create space in front of the landing, because windows are a lot thinner than the roof so, yes, we could easily improve the thermal efficiency, but this would detract from the feeling of space in the hall/landing area - it’s a galleried landing & there’s only just enough space in front of the landing to make it work as a galleried landing, so the window reveals are really helping to create much needed space.

 

The views aren’t “stunning”, but they do give us great pleasure.  The views mostly comprise lots of different kinds of trees.  There are one or two edges of other buildings visible, but we can’t see any of the other buildings’ windows, so the neighbours won’t be able to see in.  There’s a small newbuild bungalow right next door on one side, but there’s a holly hedge between us (we trim it down to around 2.3m tall when it needs it).  The house opposite, over the other side of the road, is in several acres, so all we see is the trees along their boundary with the road, & we have to look very hard to glimpse their house in the distance.  The road is a B-road & there are no pavements, so there’s very little pedestrian activity.

 

The view at the back will be our 2m high garden fence (just over 9m from the back of the house) + above this there’s a long view of trees to either side, & lots of sky, so very pleasant.  On the west side, there’s big plot again.  There’s a monster hedge on this neighbour’s side of the boundary (well maintained by the neighbour's gardeners) & all we can see of their house is the top of the roof.

[SteamyTea]

7 hours ago, Tony L said:

I’d prefer less glass. 

The building regs may force you to have less glazing.

[Adrian Walker]

10 hours ago, Tony L said:

 

I’d prefer less glass.  The purpose of the glass is, to please my partner, who wants lots of glass, especially on the façade.  It’s half her money, so I’m compromising.  I’ve deleted a lot of the glass from our original approved plan, having learnt so much here on BH over the past year.  Windows have been deleted from the sides & the south facing rear elevation.  I also persuaded her that her log burner was a daft idea for this kind of house, & the chimney has been deleted as well.

 

I’m more concerned about unwelcome solar gain in the summer months, on the east & south elevations, than I am about having to turn the heating up.

 

The glass in the sloping roof above the hall/landing could be reduced, but this is helping to create space in front of the landing, because windows are a lot thinner than the roof so, yes, we could easily improve the thermal efficiency, but this would detract from the feeling of space in the hall/landing area - it’s a galleried landing & there’s only just enough space in front of the landing to make it work as a galleried landing, so the window reveals are really helping to create much needed space.

 

The views aren’t “stunning”, but they do give us great pleasure.  The views mostly comprise lots of different kinds of trees.  There are one or two edges of other buildings visible, but we can’t see any of the other buildings’ windows, so the neighbours won’t be able to see in.  There’s a small newbuild bungalow right next door on one side, but there’s a holly hedge between us (we trim it down to around 2.3m tall when it needs it).  The house opposite, over the other side of the road, is in several acres, so all we see is the trees along their boundary with the road, & we have to look very hard to glimpse their house in the distance.  The road is a B-road & there are no pavements, so there’s very little pedestrian activity.

 

The view at the back will be our 2m high garden fence (just over 9m from the back of the house) + above this there’s a long view of trees to either side, & lots of sky, so very pleasant.  On the west side, there’s big plot again.  There’s a monster hedge on this neighbour’s side of the boundary (well maintained by the neighbour's gardeners) & all we can see of their house is the top of the roof.

Have you modelled your design in PHPP or similar?

[Tony L]

11 hours ago, SteamyTea said:

18 hours ago, Tony L said:

I’d prefer less glass. 

The building regs may force you to have less glazing.

Thanks for the warning; that hadn't occurred to me.

[Tony L]

7 hours ago, Adrian Walker said:

Have you modelled your design in PHPP or similar?

No - the design isn't yet sufficiently developed to start anything like that.

 

PHPP modelling sounded like a good idea (even though I will not reach PH standard), but then I had a quick look at PHPP modelling a while back & decided I don't have the time I'd need to learn how to do this myself, & paying somebody else to do it will likely cost more than I'm prepared to pay.  If anybody wants to tell me, I've got this wrong (or perhaps tell me I've made a reasonable decision) please do so.

[Nickfromwales]

3 minutes ago, Tony L said:

Thanks for the warning; that hadn't occurred to me.

It's in respect Part O mostly, combatting solar gain, and not wasting electricity mitigating against such issues.

[Tony L]

6 minutes ago, Nickfromwales said:

It's in respect Part O mostly, combatting solar gain, and not wasting electricity mitigating against such issues.

Good info - thanks, Nick.  I was thinking it might be because the U values may not be good enough.  I have been mindful of solar gain.  Our summers aren't getting any cooler.  All the glass you can see on the facade in the Sketchup drawing above is on the north elevation, so the low sun will just about shine through these windows for a short time in the morning as it heads around to the east elevation, & there's shading on the west side, so there will be negligible solar gain before the sun sets in the evening.  The glass area on the other three elevations adds up to less than you can see on the north elevation & there's a 1m overhang on the roof at the back of the house to give shade to the ground floor windows.

[Nickfromwales]

18 minutes ago, Tony L said:

Good info - thanks, Nick.  I was thinking it might be because the U values may not be good enough.  I have been mindful of solar gain.  Our summers aren't getting any cooler.  All the glass you can see on the facade in the Sketchup drawing above is on the north elevation, so the low sun will just about shine through these windows for a short time in the morning as it heads around to the east elevation, & there's shading on the west side, so there will be negligible solar gain before the sun sets in the evening.  The glass area on the other three elevations adds up to less than you can see on the north elevation & there's a 1m overhang on the roof at the back of the house to give shade to the ground floor windows.

There’s a consideration for both parts, but “over glazed” often raises red flags for overheating for peak summer spells.

[SteamyTea]

50 minutes ago, Tony L said:

Thanks for the warning; that hadn't occurred to me.

Always easier to say 'a big boy did it, then ran away'.

Works for me when I need to get out of a hole.

[Adrian Walker]

1 hour ago, Tony L said:

No - the design isn't yet sufficiently developed to start anything like that.

 

PHPP modelling sounded like a good idea (even though I will not reach PH standard), but then I had a quick look at PHPP modelling a while back & decided I don't have the time I'd need to learn how to do this myself, & paying somebody else to do it will likely cost more than I'm prepared to pay.  If anybody wants to tell me, I've got this wrong (or perhaps tell me I've made a reasonable decision) please do so.

 

Jeremy, who used to be on this group, had a simplified version. https://forum.buildhub.org.uk/applications/core/interface/file/attachment.php?id=76599&key=beb16589ffeb7656a272e8a689af6cac

 

Edited Thursday at 17:00 by Adrian Walker

[saveasteading]

I would advise against working to any perceived "pass" standard.

 

The people who make up these systems may be less expert than you.

Use them as a guide.

I'm not guessing....I've met some.

 

Eg I designed a building that got an SBEM of D, 15 years ago and now gets a B. With current insulation it would get A.

At the time you got bad marks for air source, and no credit for north lights. But they gave credits for wind turbines and other fads.

[SteamyTea]

3 minutes ago, saveasteading said:

the time you got bad marks for air source

That was because grid CO₂ intensity was around 700 gm/kWh, now usually below 100.

They possibly assumed that north facing windows were single glazed, not triple and argon filled. 

 

I do wish they standard were publicly available, and free. It is almost like they don't want the public to know.

[Tony L]

3 hours ago, Adrian Walker said:

Jeremy, who used to be on this group, had a simplified version. https://forum.buildhub.org.uk/applications/core/interface/file/attachment.php?id=76599&key=beb16589ffeb7656a272e8a689af6cac

 

 

Thanks for Jeremy’s spreadsheet, @Adrian Walker.  It certainly looks more straight forward than the PHPP spreadsheet I looked at, but I would have to ask a lot of questions if I were to use it to help evaluate my design, in which I am not too concerned about what’s going on downstairs, but am keen to understand what’s going on further up, where I have 3 dormers, 4 flat roofs, both north & south facing windows in the sloping roof, no heating &, if things work out well, no electric cooling either.  I think I’d still rather outsource heat loss/solar gain calcs to somebody who can do it far more quickly than me.

 

For now, I’m focusing on trying to find a competent person to take on my building regulation & construction drawings, including finalising some elements of the design.  @Nickfromwales has recommended somebody, & I’m hoping this problem will soon be solved.

[ToughButterCup]

Here's a direct answer to the title question 

https://www.theguardian.com/environment/2025/may/16/energy-bills-for-uk-new-build-homes-higher-due-to-poor-construction-standards-analysis-shows?CMP=Share_AndroidApp_Other

 

 

[JohnMo]

23 hours ago, Adrian Walker said:

I’m more concerned about unwelcome solar gain in the summer months, on the east & south elevations, than I am about having to turn the heating up

Blinds or curtains closed first, UFH or fan coils connected to heat pump second. PV to power heat pump 3rd.

 

It's sunny here and has been for a few weeks. Average temperature yesterday was 9.5 degrees and down to 2 degs overnight. However we have the cooling on and it's been on for the last month (except a few days). Well insulated, quite airtight and lots of glazing. Apart from a brief period 5pm to 7pm house stays pretty stable at 20 to 21 degs.

 

PV pays for the heat pump to run. Generally running the house, ASHP etc paying about 80p a day for electric, don't get paid for export otherwise it would be free.

 

[Thorfun]

I’d say you don’t want to negate all the solar gain! You can use it to heat the house and then block it out with external blinds. The sun is free heat after all. 

[Nick Laslett]

@Tony L, Jeremy’s spreadsheet is very easy to complete. All you need is the u-values for walls, roof, foundation, windows and door etc. All the room, window and door dimensions, the target airtightness, the target room temperature, the lowest winter outside temp for your location. 
 

Just using the data already in the spreadsheet for Jeremy’s house, you can change the airtightness to see how much this effects the energy use, or change the lowest outside temperature, or your target indoor temperature. It will give you a much better idea of how this all works together. 
 

There is plenty of discussion in the original thread on the details of how the spreadsheet works. 
 

 

My biggest takeaway when I first found BuildHub, was that you need a cooling strategy, much more than you need to worry about insulation. If you have a well built house, with good insulation and high airtightness, you will suffer from overheating. (assuming that this is not already integral to the design.)
 

You can design in many measures to reduce this, but basically any windows except those facing north will be giving you massive solar gain during the summer and after a few days all that heat in the house has nowhere to go. Jeremy found that just the heat from his UVC was enough to make his house overheat and he needed to switch to a better insulated solution for his domestic hot water to address this. 
 

MVHR will not help with cooling. You will find plenty of help from members here on this cooling topic, but the earlier you can design it in, the better.

[JohnMo]

1 hour ago, Nick Laslett said:

target airtightness

You do not add target airtightness you add air changes per hour. Lack of airtightness add to the controlled ventilation by about 5%. So airtightness of about 2 m³/m² will add 0.1 to any controlled ventilation. So 0.5 becomes 0.6. (think those numbers are about correct.

 

MVHR set recovery to about 85% anything else set to zero.

[Tony L]

4 hours ago, JohnMo said:

Blinds or curtains closed first, UFH or fan coils connected to heat pump second. PV to power heat pump 3rd.

 

It's sunny here and has been for a few weeks. Average temperature yesterday was 9.5 degrees and down to 2 degs overnight. However we have the cooling on and it's been on for the last month (except a few days). Well insulated, quite airtight and lots of glazing. Apart from a brief period 5pm to 7pm house stays pretty stable at 20 to 21 degs.

 

PV pays for the heat pump to run. Generally running the house, ASHP etc paying about 80p a day for electric, don't get paid for export otherwise it would be free.

 

 

That's good.  I've got those in the right order then.  I'm planning external motorised blinds on the two small Fakros in the two south facing bedrooms.  I'll make provision for (ie a long hole where the eaves overhang) external Venetian blinds for the French windows to the patio.  I don't think my budget will allow for PV.  I'd really rather just plan to work a few more months before I retire & have some PV, but my partner doesn't like that plan, so I'll give her that one & I won't feel so bad about overruling her wishes when something really important comes up.

[Tony L]

2 hours ago, Nick Laslett said:

My biggest takeaway when I first found BuildHub, was that you need a cooling strategy, much more than you need to worry about insulation. If you have a well built house, with good insulation and high airtightness, you will suffer from overheating. (assuming that this is not already integral to the design.)
 

You can design in many measures to reduce this, but basically any windows except those facing north will be giving you massive solar gain during the summer and after a few days all that heat in the house has nowhere to go. Jeremy found that just the heat from his UVC was enough to make his house overheat and he needed to switch to a better insulated solution for his domestic hot water to address this. 

 

Thank you very much for your post, @Nick Laslett.  I am persuaded I should spend time on Jeremy's spreadsheet as soon as the time can be found.  At the very least, I will read the thread about how it all works.  I have considered a plan for summer hot air purge, involving a small as possible window at the highest point on my east gable, which is shaded from the afternoon/evening sun (& can have the glass fully covered anyway). The window will connect to a vent duct, with a super efficient fan inside, that will suck air from near the apex of the vaulted ceiling above the landing & dump it outside.  I'll open a downstairs window.  I can see this being more effective than just opening a few windows, & it could be left to run when the house is unoccupied.  Good idea/bad idea?  I haven't fully thought this through yet.

[Tony L]

3 hours ago, Nick Laslett said:

MVHR will not help with cooling. 

 

Not even a little bit?  What am I not understanding here: I'd have thought that if the air outside is cooler than the air inside & my MVHR system is taking warm air from inside, bypassing the heat exchanger in summer mode, & replacing the exhaust air with cool air from outside, this will help keep the inside temperature lower.  Of course, MVHR won't be the entire answer to the summer overheating problem, but I think it must be having some effect.