Q&A on our self-build, as featured on Grand Designs 2024

[thefoxesmaltings]

As promised, a Q&A, to ask us anything about our Grand Designs project, which aired on TV two weeks ago.

 

Forums like Buildhub, have been an great resource for us to learn from others, and so if this is one way we can give back, then happy to.

 

Much of the 'technical' gets glossed over during the TV show, purely due to time constraints. So if there are specific questions about our building fabric, fire away.

 

Rather than dumping loads of photos here, there's plenty of the process on our Instagram: https://www.instagram.com/thefoxesmaltings/

Disclaimer: We are first time self-builders, and I am by no means an expert, nor do I pretend to be one. There is still plenty of stuff I have no idea about, and plenty of you on here with way more knowledge than me!

 

Based on any answers, I would love to know what you would have done differently, or things we could have done better. Who knows, there might be a next project...

And of course, if you missed the episode, you can watch it on demand, on Channel4.com.

[twice round the block]

Just been through your Instagram posts, very informative and some great links.

Nice finishing and attention to detail  within the build.

Congratulations you've achieved a lovely home through the stress that goes hand in hand with self building.

[thefoxesmaltings]

One thing that might help, and I forgot to add into the original post is a breakdown of the house technicals. Off the top of my head...

• Block & Beam subfloor.
• Timber frame to 0.09 wall U-value. (220mm insulation to walls. 150mm to roof).
• Double glazing, with solar glass spec to large south facing units.
• Brick clad and slate roof.
• MVHR + Comfoclime Cooling and heating.
• Air Source Heat Pump
• 10kW PV System, 10kW Battery Store & EV Charger.
• UFH Upstairs & downstairs.
• Energy rating of A.
• Air Tightness of 2.22.

[garrymartin]

Amazing property. Recorded the programme whilst on holiday and watched it on our return. Well done.

 

Can I ask, is it wet underfloor heating throughout using the ASHP? If so, what is your first-floor build-up?

[zzPaulzz]

I was wondering about the performance numbers, thanks for sharing. Did you add more insulation over the insulation we saw set into the frame? We couldn’t find a TF company that could achieve 0.09 without extra layers of PIR. Triple glazing seems to be the next step for efficiency but I guess with your widows that would have been very expensive? 

[Iceverge]

3 hours ago, zzPaulzz said:

I was wondering about the performance numbers, thanks for sharing. Did you add more insulation over the insulation we saw set into the frame? We couldn’t find a TF company that could achieve 0.09 without extra layers of PIR. Triple glazing seems to be the next step for efficiency but I guess with your widows that would have been very expensive? 

 

In terms of energy saving I did the numbers a couple of years ago. 

 

The best bang for your buck beyond bregs basics are:

 

1. Airtighess 

2. MVHR

3. 3g Windows 

4. Roof insulation

5. Wall insulation

6. Floor insulation

 

In terms of better performance than basic on a TF you could stick frame it on site and build whatever you like.

Edited October 16 by Iceverge

[ChrisInKent]

6 hours ago, thefoxesmaltings said:

 

• Air Source Heat Pump

Thanks for sharing the stats. Just wondered how many sqm is your house and what size ASHP you ended up with?

[thefoxesmaltings]

On 16/10/2024 at 15:03, garrymartin said:

Amazing property. Recorded the programme whilst on holiday and watched it on our return. Well done.

 

Can I ask, is it wet underfloor heating throughout using the ASHP? If so, what is your first-floor build-up?

Thanks - glad you enjoyed it.

Yes wet underfloor heating throughout. The first-floor build up is Open posi joists, 22mm egger protect chipboard, 15mm insulated UFH board to which the underfloor heating pipes were laid in. These insulated UFH boards were contact adhesive, and mechanically fixed down to the primed chipboard. Then we installed 14mm engineered wood onto this, which had to be glued down.
 

[thefoxesmaltings]

On 16/10/2024 at 15:26, zzPaulzz said:

I was wondering about the performance numbers, thanks for sharing. Did you add more insulation over the insulation we saw set into the frame? We couldn’t find a TF company that could achieve 0.09 without extra layers of PIR. Triple glazing seems to be the next step for efficiency but I guess with your widows that would have been very expensive? 

The TF company (Turner Timber) had an additional insulation package, which they affixed onsite. probably not shown on the program - 100mm to the internal face of the walls. 120mm which was already in the frame.

Yeah triple glazing was out of the question for us, mostly due to budget and the sheer size of some of our panes. The largest being 4.5m x 3.1m high. These weighed 750kg alone, so to have gone down the triple glazing route, would have meant additional structural engineering costs and probably beefing up the steel.

[thefoxesmaltings]

On 16/10/2024 at 20:52, ChrisInKent said:

Thanks for sharing the stats. Just wondered how many sqm is your house and what size ASHP you ended up with?

No probs. - 400sqm house and a 14kW Daikin Altherma 3ph ASHP.

[JamesP]

On 16/10/2024 at 15:26, zzPaulzz said:

I was wondering about the performance numbers, thanks for sharing. Did you add more insulation over the insulation we saw set into the frame? We couldn’t find a TF company that could achieve 0.09 without extra layers of PIR. Triple glazing seems to be the next step for efficiency but I guess with your widows that would have been very expensive? 

Enclosed is TT wall buildup. With typo (1000mm).

[zzPaulzz]

1 hour ago, thefoxesmaltings said:

The TF company (Turner Timber) had an additional insulation package, which they affixed onsite. probably not shown on the program - 100mm to the internal face of the walls. 120mm which was already in the frame.

Yeah triple glazing was out of the question for us, mostly due to budget and the sheer size of some of our panes. The largest being 4.5m x 3.1m high. These weighed 750kg alone, so to have gone down the triple glazing route, would have meant additional structural engineering costs and probably beefing up the steel.

Hah, now you've made me go back to check my quote from Turner!  And yes, I have that wrong.  I confused them with Fleming (who only supply the additional insulation). Going to double check now that I've made the right decision to go elsewhere. Still time

 

Did Turner also provide you with an insulated roof? 

 

Your choice of 0.09 for the walls will go some way to mitigate the thermal loss from your windows. What U values did you end up with for your glazing? 

[Alan Ambrose]

Apologies, I'm  bit slow getting to this (I'm a bit slow getting to most things) :).

 

Just watched the programme. Congrats, a v. nice build.

 

A couple of misc questions:

 

+ what wood is the pergola?

+ which company did your corten steel cutting?

[thefoxesmaltings]

On 18/10/2024 at 16:40, zzPaulzz said:

Hah, now you've made me go back to check my quote from Turner!  And yes, I have that wrong.  I confused them with Fleming (who only supply the additional insulation). Going to double check now that I've made the right decision to go elsewhere. Still time

 

Did Turner also provide you with an insulated roof? 

 

Your choice of 0.09 for the walls will go some way to mitigate the thermal loss from your windows. What U values did you end up with for your glazing? 

Yes, Turners also provided us with an insulated roof - 150mm, in both the pitched and flat roof sections. They also provided us with the loft roll insulation (which we installed ourselves) in the raised tie truss areas.

Double glazing U values vary, as the thickness of the frame contributes slightly - around 1.1 W/m²k.

[thefoxesmaltings]

16 hours ago, Alan Ambrose said:

Apologies, I'm  bit slow getting to this (I'm a bit slow getting to most things) :).

 

Just watched the programme. Congrats, a v. nice build.

 

A couple of misc questions:

 

+ what wood is the pergola?

+ which company did your corten steel cutting?

Thanks. Appreciate it.

Pergola is Glulam - we have to treat it every year, which is slightly annoying. The cost for this in oak was astronomical, and just completely not viable.

Corten fabrication was done by Cambridge Corten.

[haythorn_1]

On 16/10/2024 at 14:17, thefoxesmaltings said:

Air Tightness of 2.22.

I’m surprised this isn’t higher given the clips you have on instagram of your air tightness tape detailing.

 

Not trying to be negative and is still very good, but the other figures you have are basically passive house level.

 

Was this intentional?

[thefoxesmaltings]

2 hours ago, haythorn_1 said:

I’m surprised this isn’t higher given the clips you have on instagram of your air tightness tape detailing.

 

Not trying to be negative and is still very good, but the other figures you have are basically passive house level.

 

Was this intentional?

No negativity taken at all. To be honest what mostly let's us down is the gym/garage door - It is insulated, and has a "seal" at the bottom, but is by no means a 'passivhaus' rated or designed door. Partly due to the fact that we couldn't find any roller doors which met this standard. And we couldn't have a sectional door overhead, as the MVHR ductwork was in the way.

 

There was also no loft hatch in place at the time of the air test. Albeit the internal loft is sealed, the air tester said it would make a difference, but I don't know if that is true.

Being first-timers, we didn't know that typically you can do an air test before everything is boarded/sealed up, to find and remediate leaks, and then do the final one at the end to get the as-is value. Lessons learned for next time, I suppose.

[joth]

36 minutes ago, thefoxesmaltings said:

No negativity taken at all. To be honest what mostly let's us down is the gym/garage door - It is insulated, and has a "seal" at the bottom, but is by no means a 'passivhaus' rated or designed door. Partly due to the fact that we couldn't find any roller doors which met this standard. And we couldn't have a sectional door overhead, as the MVHR ductwork was in the way.

 

There was also no loft hatch in place at the time of the air test. Albeit the internal loft is sealed, the air tester said it would make a difference, but I don't know if that is true.

Being first-timers, we didn't know that typically you can do an air test before everything is boarded/sealed up, to find and remediate leaks, and then do the final one at the end to get the as-is value. Lessons learned for next time, I suppose.

 

>To be honest what mostly let's us down is the gym/garage door

That's not so surprising then, although what is more surprising is that the garage was included inside the thermal envelope at all, at design stage. As a garage you certainly wouldn't and even as a gym, I wouldn't expect it needs to be at the same temperature as the rest of the house.

 

Can a more airtight boundary be made between garage and house - especially around any connector door? While it may not make difference to the bottom line airtightness figure, it may make a big difference for heating efficiency in practice.

 

 

The thing about needing to know to do 2 tests is something every architect / builder / TF supplier / MVHR supplier _should_ know  and convey to you. It's just a shame very few would. 

 

But to add to others already did say - very impressive build and such a strong attitude you both carried through it. Not easy to come through it unscathed - I know!

 

 

[thefoxesmaltings]

8 minutes ago, joth said:

 

>To be honest what mostly let's us down is the gym/garage door

That's not so surprising then, although what is more surprising is that the garage was included inside the thermal envelope at all, at design stage. As a garage you certainly wouldn't and even as a gym, I wouldn't expect it needs to be at the same temperature as the rest of the house.

You are right. It doesn't need to be the same temperature as the house, and is a unheated space. It's still got the same 220mm insulation in the walls though (minus the garage door itself), so even if cold outside, it does tend to stay fairly warm. It hasn't dropped below 17c this year since the start of Autumn, but I expect will, once we get into the deep of winter.

 

10 minutes ago, joth said:

 

Can a more airtight boundary be made between garage and house - especially around any connector door? While it may not make difference to the bottom line airtightness figure, it may make a big difference for heating efficiency in practice.

Potentially - it's a fire door which the garage/gym can directly be accessed from the house. Maybe it's as simple as a rubber gasket being places all around? Something to explore...

 

12 minutes ago, joth said:

The thing about needing to know to do 2 tests is something every architect / builder / TF supplier / MVHR supplier _should_ know  and convey to you. It's just a shame very few would. 

Sadly we weren't told by anyone, or those above trades. C'est la vie. Arguably, it's my fault as project manager for not knowing better or doing my research on that. I suppose we lucked out in that sense of achieving a 2.2 rating, having not done a prior test.