Can part of a house be declared as outside the thermal envelop?

[epsilonGreedy]

About 6% of the internal floor area of my house is within a single story extension that abuts to the main house. Inside the extension there is a small entrance hall 2.5m x 2.5m plus the downstairs toilet 2.5m x 1m.

 

I do not intend to heat this area above 15 degrees if at all.

 

If I could declare this part of the house as outside SAP calculation area I could save a few ££'s on the external door. There is a fullfill insulated 100mm cavity wall between the main house and the single story section. 

[PeterW]

Why would you ..? It will drop over time to equilibrium if you are not careful and don’t provide heat. You’re not going to save much anyway as an external door is more about weather resistance and security than insulation and you can get a decent hardwood door for £150 ex VAT. 

[joe90]

My porch is outside the thermal envelope, just there as an airlock, protect nice oak ( insulated ) door, to take off muddy boots etc but I would not want a wc to be-in one.

Edited February 4, 2021 by joe90

[the_r_sole]

you'd just have to move the door doing the thermal separation into the house, so no big saving on having the door in a different location.

Not sure why you'd want to not heat the toilet either, is this a conversion project?

[epsilonGreedy]

On 04/02/2021 at 09:49, PeterW said:

Why would you ..? It will drop over time to equilibrium if you are not careful and don’t provide heat. You’re not going to save much anyway as an external door is more about weather resistance and security than insulation and you can get a decent hardwood door for £150 ex VAT.

 

 

One reason is our expensive taste in doors. When the sash window company quoted for the windows they added quotes for wooden doors. The price was over £1000 for a semi glazed stable door with 9-pane Georgian window panel. Sub £250 would be great.

 

Something like this:

 

 

The door will be our primary entrance door.

 

I thought SAP conformance was a reason for the high price, I had not considered the weather resistance and security cost elements you mention.

 

 

Edited February 5, 2021 by epsilonGreedy

[epsilonGreedy]

On 04/02/2021 at 11:15, joe90 said:

My porch is outside the thermal envelope, just there as an airlock, protect nice oak ( insulated ) door, to take off muddy boots etc but I would not want a wc to be-in one.

 

 

Ok this indicates that such self declaration is possible, thanks for posting. I would ensure that provision is made for retrofitting a radiator if the unheated equilibrium temperature mentioned by @PeterWis much below 15 degrees in winter.

 

Thinking more about this, if the extension is a 6 sided cube shedding heat on 5 sides it will get chilly. Some heat will leach through the floor slab from the UFH on the other side of the internal door then the U 0.28 cavity wall will shed a bit more heat into this space. 

[epsilonGreedy]

On 04/02/2021 at 11:25, the_r_sole said:

you'd just have to move the door doing the thermal separation into the house, so no big saving on having the door in a different location.

Not sure why you'd want to not heat the toilet either, is this a conversion project?

 

 

The intermediate internal door does not have to be stylistically fancy unlike the real exterior door. I have not looked at new build door SAP regs, I am guessing the U should be 1.6 or or 1.8.

 

My build is a new build not a conversion.

 

Anyhow thanks for the feedback, I am just exploring the regulatory boundary at the moment and also thought excluding the entrance hall extension would deliver a few bonus points on the final EPC rating.

[ProDave]

I guess our sun room is outside the thermal envelope.  It has a Rationel "external" French door pair between the house and the sun room, it will have no heating and no mvhr (so the windows in the sun room will have trickle vents)

 

I don't recall how it was dealt with on the SAP calculations though.

[the_r_sole]

24 minutes ago, epsilonGreedy said:

 

The intermediate internal door does not have to be stylistically fancy unlike the real exterior door. I have not looked at new build door SAP regs, I am guessing the U should be 1.6 or or 1.8.

 

My build is a new build not a conversion.

 

Anyhow thanks for the feedback, I am just exploring the regulatory boundary at the moment and also thought excluding the entrance hall extension would deliver a few bonus points on the final EPC rating.

 

It doesn't have to be stylish but it still needs to be an external door, most of what you are paying for is the insulation/security side of things anyway. I find it strange to be building a badly performing area into a new house, but you'll have to construct it in such a way as the floor screed can't run through - I don't think a £750 saving on a door would ever encourage me to have a cold toilet! ?

I think it's counter intuitive to say you've got a great epc rating on the house, but there's areas of it that are unheated so they don't count

[epsilonGreedy]

3 minutes ago, the_r_sole said:

I think it's counter intuitive to say you've got a great epc rating on the house, but there's areas of it that are unheated so they don't count

 

 

It is counter intuitive, they would be vanity EPC points I accept.

 

The real saving will come from running the extension 5 degrees cooler than the rest of the house and not extending the UFH into what is a small floor peninsular with a high perimeter ratio.

 

10 minutes ago, the_r_sole said:

I find it strange to be building a badly performing area into a new house, but you'll have to construct it in such a way as the floor screed can't run through - I don't think a £750 saving on a door would ever encourage me to have a cold toilet! 

 

 

There will be 140mm of xps insulation under the floor screed, 0.36 U in the 100mm cavity and 300mm in the cold loft space above. Given a short truss span and a 30 degree pitch it will be difficult to get much more loft insulation in without completely choking the attic space. So not exactly bad and not stella by BuildHub standards, just within regs if it was heated.

 

The complex shape of the house to blend in with a conservation area and our budget mean the house will perform well short of a passiv house but your typical Passiv house owner does not get to see alpacas and haltered sheep being taken for walks around the village or see a vintage horse & trap passing by through a Georgian sash window.

[the_r_sole]

It's a strange one for me, I've never had a client ask for an unheated toilet in their new house to either achieve a higher epc rating or to save a small percentage of the cost of a door, but each to their own I guess.

[A_L]

41 minutes ago, the_r_sole said:

achieve a higher epc rating

 

Moving the external door inwards will increase the exposed perimeter and reduce the floor area leading to a higher floor U-value. There will be an increase in the external wall area leading to a higher heat loss, the newly 'externalised' wall may also be thermally inferior to the original external wall. The changes would also increase the allowance for thermal bridging. All factors which lead to a poorer epc