UFH design etc.

[matthyde83]

Hi all - due to start on site in February and trying to make some decisions. 

 

New build in brick and block.  150mm cavity with EPS beads planned.  Current floor build up from architect 150mm slab, 150mm insulation, 75mm screed.  Thinking ASHP. 
 

Questions -

 

Should I increase the insulation in the floor by 50mm and go for a flowing screed at 50mm? I’m looking at porcelain tiles for majority of downstairs. They’re likely to be 20mm though as have landscaping done and want the same. 

 

Recommended UFH supplier/designer?

 

How do I work out if I’ll need heating upstairs?  Read a lot of posts and suggestions it’s not needed but the females in my life are dubious…

[Moonshine]

40 minutes ago, matthyde83 said:

Hi all - due to start on site in February and trying to make some decisions. 

 

New build in brick and block.  150mm cavity with EPS beads planned.  Current floor build up from architect 150mm slab, 150mm insulation, 75mm screed.  Thinking ASHP. 
 

Questions -

 

Should I increase the insulation in the floor by 50mm and go for a flowing screed at 50mm? I’m looking at porcelain tiles for majority of downstairs. They’re likely to be 20mm though as have landscaping done and want the same. 

 

Recommended UFH supplier/designer?

 

How do I work out if I’ll need heating upstairs?  Read a lot of posts and suggestions it’s not needed but the females in my life are dubious…

 

50mm liquid screed and increase insulation to 175mm. Though it will need to be sanded for tiles to go onto the screed.

 

I think heating is needed upstairs, it is what I am doing. Either radiators or aluminium spreader plates screwed under floor boards.

 

Where in the uk are you?

[joth]

Yes I'd increase the under floor insulation as far as you can. (why not dig out a bit deeper?)

 

Regarding upstairs, 150mm EPS bead is only about 0.17 U-value. People talking about having no heating upstairs are in near passive houses, so around 0.10 U-value. We have a mix of build type in our retrofit, 0.10 - 0.13, and even so the guest room drops to >17°C when unoccupied. (Putting humans inside the rooms is actually the primary heat source).

There's masses of variables here though. E.g. where in the UK are you? do you just have bedrooms upstairs (that typically should be kept 1-2 ° cooler) or other types of room? How much glazing, and what orientation? What is the internal wall build up and how much isolation between rooms due to shape and layout of building? Do you have MVHR? Etc.

Strongly advise gathering all that info and then getting a room by room heat loss calculation done, which will give a clear guide how much you'll be spending heating those rooms.

But yes, without improving the building quality I'm sure you'll need some sort of heating upstairs.

HTH

 

[PeterW]

150mm of PIR is fine - but as everyone else is saying, why not dig down further ..?

 

If you go with 150mm of beads why don’t you also go with 25mm of PIR inside the walls too which gives you a decent level and also adds a space for wiring etc 

[matthyde83]

2 hours ago, Moonshine said:

 

50mm liquid screed and increase insulation to 175mm. Though it will need to be sanded for tiles to go onto the screed.

 

I think heating is needed upstairs, it is what I am doing. Either radiators or aluminium spreader plates screwed under floor boards.

 

Where in the uk are you?

 

We're in Surrey, just inside M25.

[matthyde83]

1 hour ago, joth said:

Yes I'd increase the under floor insulation as far as you can. (why not dig out a bit deeper?)

 

Regarding upstairs, 150mm EPS bead is only about 0.17 U-value. People talking about having no heating upstairs are in near passive houses, so around 0.10 U-value. We have a mix of build type in our retrofit, 0.10 - 0.13, and even so the guest room drops to >17°C when unoccupied. (Putting humans inside the rooms is actually the primary heat source).

There's masses of variables here though. E.g. where in the UK are you? do you just have bedrooms upstairs (that typically should be kept 1-2 ° cooler) or other types of room? How much glazing, and what orientation? What is the internal wall build up and how much isolation between rooms due to shape and layout of building? Do you have MVHR? Etc.

Strongly advise gathering all that info and then getting a room by room heat loss calculation done, which will give a clear guide how much you'll be spending heating those rooms.

But yes, without improving the building quality I'm sure you'll need some sort of heating upstairs.

HTH

 

 

Digging out deeper is definitely possible.  We are demolishing a bungalow in its place.  Is a sand and cement 75mm screed better than going for 50mm flowing then?

 

Just bedrooms (and bathrooms upstairs).  We're in Surrey.  Standard sized windows on 4 bedrooms, both east and west facing (west to rear).  Master in centre with doors to a covered balcony.  Yes to MVHR.  I've uploaded an upstairs floorplan.  Not finalised yet.

 

 

53C.pdf

[matthyde83]

27 minutes ago, PeterW said:

150mm of PIR is fine - but as everyone else is saying, why not dig down further ..?

 

If you go with 150mm of beads why don’t you also go with 25mm of PIR inside the walls too which gives you a decent level and also adds a space for wiring etc 

 

That is an option.  Obviously we lose room size, but not much.  I was planning wet plaster for airtightness though so that's going to put pay to that...

[PeterW]

Use a sand / cement parge coat on the blockwork first ..? Then you’ve got options. 

[joth]

1 hour ago, matthyde83 said:

  I was planning wet plaster for airtightness though so that's going to put pay to that...

Unless you really micromanage your trades (or DIY everything), this is pretty much impossible in the UK,  IMHO. Every electrician/plumber/decorator/joiner/kitchen fitter/etc etc needs to know not to puncture the plaster, or know how to use unfamiliar airtight fittings and techniques wherever they do. Plus there's the long-term longevity of that strategy.

 

We had OSB3 (smartply) for airtightness, then 25mm service void then plasterboard, and even here it was tough work ensuring everything from intentional penetrations (outside taps, lights, ASHP pipes) to slips with a multitool that hit the OSB got remedial work needed.

 

Not saying it's impossible, just a matter of whether the project style actually supports it

 

[joth]

2 hours ago, matthyde83 said:

 

Digging out deeper is definitely possible.  We are demolishing a bungalow in its place.  Is a sand and cement 75mm screed better than going for 50mm flowing then?

 

Just bedrooms (and bathrooms upstairs).  We're in Surrey.  Standard sized windows on 4 bedrooms, both east and west facing (west to rear).  Master in centre with doors to a covered balcony.  Yes to MVHR.  I've uploaded an upstairs floorplan.  Not finalised yet.

 

 

53C.pdf 333.58 kB · 2 downloads

 

Looks a good "square" shape so quite possible to get good level of heat retention. There's some thick walls separating upstairs to three areas (B2&5, B3&4, and master+stair void), so at very least you'll want to consider those three "zones" for heating needs. To really do any heat loss analysis you'd need plans for the other floors too, to see losses/gains between floors.

 

Honestly I can't believe that architects don't do this already. Heat loss calcs probably take 2 hours of training to learn how to do, and 20mins to complete once they're familiar with it,  and the architect already has 100% of the data needed to do it right under their nose anyway. And having the heat loss calcs is an important tool in the iterative design process.

RIBA really are sitting on their hands while the planet burns.

 

Edited December 8, 2021 by joth

[Bitpipe]

9 minutes ago, joth said:

Unless you really micromanage your trades (or DIY everything), this is pretty much impossible in the UK,  IMHO. Every electrician/plumber/decorator/joiner/kitchen fitter/etc etc needs to know not to puncture the plaster, or know how to use unfamiliar airtight fittings and techniques wherever they do. Plus there's the long-term longevity of that strategy.

 

We had OSB3 (smartply) for airtightness, then 25mm service void then plasterboard, and even here it was tough work ensuring everything from intentional penetrations (outside taps, lights, ASHP pipes) to slips with a multitool that hit the OSB got remedial work needed.

 

Not saying it's impossible, just a matter of whether the project style actually supports it

 

 

Unless you're achieving a passive standard of insulation & airtightness you will likely need heating in the bedrooms. We have not needed it and only have UFH on ground floor - nothing in basement and low power electric UFH and wet towel rails in upstairs bathrooms.

 

However, laudable that you want to maximise the insulation and airtightness. which really needs considered from day one and closely monitored to make sure it's not compromised.

 

The most challenging aspect are  floor / wall interfaces and your roof space if you're having a cold roof.

 

For our timber frame build, there is a layer of airtightness sheet that is taped to the top of the inside wall (which itself is airtight) and goes out around the floor junction and back inside where it meets the inside bottom of the upper wall. Everything taped with the special tapes. Others can advise on how you achieve this with brick and block.

 

Windows and doors have compriband tape and are taped on the inside to the inner airtightness layer.

 

There is a service cavity of 50mm battens applied to the interior wall to minimise penetrations through the airtightness layer. Any penetrations through the walls (like ducts for lighting etc, are sealed and taped on the inside.

 

Obviously for passive standard, which I get you're not trying to achieve, you need to forgo cat flaps and letter boxes, also window trickle vents and traditional extractor fans (using MVHR instead).

 

 

 

 

[PeterW]

2 minutes ago, joth said:

Honestly I can't believe that architects don't do this already. Heat loss calcs probably take 2 hours of training to learn how to do, and 20mins to complete once they're familiar with it,  and the architect already has 100% of the data needed to do it right under their nose anyway. And having the heat loss calcs is an important tool in the iterative design process.

That is quite an underestimate of the time to do a full heat loss calculation. You need to understand every room, every structural element and all unheated spaces and then the materials used. Whilst they have this (assuming all is CAD) there are limited M&E tools that can auto import a full layered CAD system to do this out of the box. 
 

Given most plumbers still use Mears calculators it’s not exactly a science and a lot more of an art…

 

https://mhmear.co.uk/product/first-principles-domestic-central-heating-calculator/

[joth]

1 hour ago, PeterW said:

That is quite an underestimate of the time to do a full heat loss calculation. You need to understand every room, every structural element and all unheated spaces and then the materials used. Whilst they have this (assuming all is CAD) there are limited M&E tools that can auto import a full layered CAD system to do this out of the box. 
 

Given most plumbers still use Mears calculators it’s not exactly a science and a lot more of an art…

 

https://mhmear.co.uk/product/first-principles-domestic-central-heating-calculator/

Yeah, I'm definitely not suggesting they complete a full PHPP model, but the thing MCS installers do (or the Jeremy Harris sheet from this forum) is fairly limited in the granularity it goes down to and an architect could whizz through it fairly quickly after they've done it a few times, I'm sure. (The first time anyone does it it'd definitely take longer, but that makes it even more surprising that architects aren't). (My suspicion is most would start out copying the one from the most similar house they previously worked on, and then editting as needed).

 

You don't really need M&E knowledge/tools as the goal is not designing heating solutions, just calculating the room by room heat demand.