New member trying to improve energy performance - Belfast

[Mr Ben]

Hi All, 

 

Many thanks for all the incredibly useful advice here!

 

Brief introduction - buying a ~300m2 new build from developer. House is beam / block construction with a cold roof, and was already watertight before we first viewed it in the Spring. It's not been designed to be particularly energy efficient (when questioned their target air tightness was "better than 5m3/h/m2"), but developer has a good reputation and they've been relatively tolerant of my requests such as improved air permeability and replacing gas boiler with ASHP. I feel like a bit of a fraud compared to the many true self builders on here, however dealing with a developer and an existing shell has definitely presented its own set of challenges. 

 

Have ended up with a 12kW Panasonic Aquarea monobloc, a 300L mixergy tank, and pipework at 150mm centres with minimal zoning rather than a stat in every single room. Air tightness is being addressed with a combination of rubber paint to exposed blockwork, vapour barrier membrane over joists, wet plaster throughout and an additional / intermediate pressure door test, with the aim of improving to under 1. 

 

Current preoccupations are how to insulate under attached garage floor, and how to monitor floor temperatures. Not sure if I should start new threads to ask for advice, or if its ok to post some questions in the introduction thread. 

 

[Declan52]

Welcome.

For a start the feeling that your a fraud is not true. Few here have done the complete build themselves with the vast majority handing the build over to a contractor or overseeing the job themselves until it gets to a point at which their skills allow them to take over and complete the build.

Why do you need to insulate under the garage floor??

Is the garage attached to the house??

You don't really need to monitor the floor temperatures. I've been running ufh in mind for near 8 years without them. I use a room stat to monitor the room temp and then call for the ufh to start it is needed. Unless your really into data logging everything in detail then it's not really needed.

For any questions you need help answering just post the question in the relevant section.

[SteamyTea]

My concern is how much insulation is fitted under the floor.

If there is not enough, it could be costly to run an ASHP.

[JohnMo]

So you have improved airtightness what have you done about ventilation?

 

 

[Mr Ben]

Thanks Declan, 

 

I want to add UFH pipes with the aim of keeping garage temp in the low teens year round for man cave activities, in particular home brewery and bike trainer. Garage was included in heat loss calcs / system design, and thermostat and manifold have already been installed. It's 5.5 x 6m, 100mm PIR in wall cavities and 400mm rockwool in loft, well insulated sectional door (Hormann). The standard spec is for 100mm slab of c30 concrete. 

 

After much deliberation builder is proposing 60mm of 300kPa XPS with a λ of 0.036, and 60mm of thermal screed for an additional £4000. I'm limited by NI building regs requiring 100mm threshold between garage and main house, which BCO is apparently interpreting as strict 100mm change in floor levels, so pretty restricted in total floor height. Concerned that's a lot of money for not a lot of insulation, and not a lot of thermal mass. Thermal stability is as important as absolute energy use, in my head I'd rather have concrete with a lower emissivity than a thermal screed designed to turn on and off like a radiator.

 

Ideally I'd like to use 50mm of 150kPa PIR with λ 0.022 under 75mm of concrete. I can't find a lot of information on compressive strength needed under a garage slab, most of what's online seems to be converting a garage into habitable space. Sanity check, if my car weighs 2200kg and I jack up half of that weight on a scissor jack with a 13 x 25cm footplate that adds 3300kg / m2 of pressure, or 33kPa, just over 1/5th of what would compress insulation by 5mm, before even considering the safety margin in the insulation product and the load spreading of a concrete slab.

 

Question - does this seem like a reasonable approach? 

[Mr Ben]

10 minutes ago, JohnMo said:

So you have improved airtightness what have you done about ventilation?

 

 

MVHR is Brink Renovent Excellent 400L

[Mr Ben]

58 minutes ago, SteamyTea said:

My concern is how much insulation is fitted under the floor.

If there is not enough, it could be costly to run an ASHP.

 

This is my main concern, although for a target temperature of 10-15 degrees and an otherwise pretty well insulated structure I don't imagine it'll take an awful lot of heating for most of the year. Part of me wonders if adding insulation is going to make more problems with overheating in the summer, and whether I'd be better just insulating the slab along the two exterior sides to get more thermal mass in the form of concrete. I presume not because the bison beams would still act as massive cold bridges

[Declan52]

56 minutes ago, Mr Ben said:

Thanks Declan, 

 

I want to add UFH pipes with the aim of keeping garage temp in the low teens year round for man cave activities, in particular home brewery and bike trainer. Garage was included in heat loss calcs / system design, and thermostat and manifold have already been installed. It's 5.5 x 6m, 100mm PIR in wall cavities and 400mm rockwool in loft, well insulated sectional door (Hormann). The standard spec is for 100mm slab of c30 concrete. 

 

After much deliberation builder is proposing 60mm of 300kPa XPS with a λ of 0.036, and 60mm of thermal screed for an additional £4000. I'm limited by NI building regs requiring 100mm threshold between garage and main house, which BCO is apparently interpreting as strict 100mm change in floor levels, so pretty restricted in total floor height. Concerned that's a lot of money for not a lot of insulation, and not a lot of thermal mass. Thermal stability is as important as absolute energy use, in my head I'd rather have concrete with a lower emissivity than a thermal screed designed to turn on and off like a radiator.

 

Ideally I'd like to use 50mm of 150kPa PIR with λ 0.022 under 75mm of concrete. I can't find a lot of information on compressive strength needed under a garage slab, most of what's online seems to be converting a garage into habitable space. Sanity check, if my car weighs 2200kg and I jack up half of that weight on a scissor jack with a 13 x 25cm footplate that adds 3300kg / m2 of pressure, or 33kPa, just over 1/5th of what would compress insulation by 5mm, before even considering the safety margin in the insulation product and the load spreading of a concrete slab.

 

Question - does this seem like a reasonable approach? 

Might be easier to lift blocks out of the floor and insulate it from underneath 

Or the easiest method is have none and accept it's going to be slightly cooler when you go in. If your working on your car then buy a blow heater which will heat the room very quickly. Your really only talking about a few hours at a time. If your on your bike then your going to be warm enough. Your main heat loss will be through the garage door so might be better to spend extra here on a quality door to help keep the heat in.

To spend £4000 on insulation to heat a room your only going to use occasionally is a bit crazy. 

[JohnMo]

Electric panel heater on a timer and thermostat. May be just as cheap to run, needs less floor insulation.

[Mr Ben]

56 minutes ago, Declan52 said:

Might be easier to lift blocks out of the floor and insulate it from underneath 

Or the easiest method is have none and accept it's going to be slightly cooler when you go in. If your working on your car then buy a blow heater which will heat the room very quickly. Your really only talking about a few hours at a time. If your on your bike then your going to be warm enough. Your main heat loss will be through the garage door so might be better to spend extra here on a quality door to help keep the heat in.

To spend £4000 on insulation to heat a room your only going to use occasionally is a bit crazy. 

 

You're probably right. What I really want is thermal stability for fermenting and storing beer rather than a comfortable workshop temperature for a few hours. 

 

[Mr Ben]

5 minutes ago, JohnMo said:

Electric panel heater on a timer and thermostat. May be just as cheap to run, needs less floor insulation.

In my head it makes more sense to use ASHP to heat the floor and gain the benefit of its COP. May also need to cool in the summer.

[JohnMo]

With poor insulation under the UFH pipes you will spend as much heating any void below or ground below, as you do heating room. Plus with an insulating screed your flow temps will need to be high also and on for a long time to have any effect on the room, so it's a loose, loose situation.  Your ASHP flow temps will be set to manage the floor heat loss of your garage, so CoP will be way worse than its needs to be.  Electric heater on 20 to 30 mins on to heat room, then click on off using next to no electricity.

[JohnMo]

Or fan coil unit, for heat and cool. Make best of CoP and cooling ability.

[Conor]

Just now, Mr Ben said:

In my head it makes more sense to use ASHP to heat the floor and gain the benefit of its COP. May also need to cool in the summer.

 

You've next to no insulation in the floor, you'll lose a colossal amount of energy to the ground. Forget the whole thermal mass thing, doesn't really make a difference.

[Mr Ben]

9 minutes ago, Conor said:

 

You've next to no insulation in the floor, you'll lose a colossal amount of energy to the ground. Forget the whole thermal mass thing, doesn't really make a difference.

Thanks Conor. 50mm of PIR would give me a u value of 0.25, it's far from ideal but surely enough to make the >300% efficiency of heating with ASHP worthwhile over a plug in electric heater?

[Conor]

3 minutes ago, Mr Ben said:

Thanks Conor. 50mm of PIR would give me a u value of 0.25, it's far from ideal but surely enough to make the >300% efficiency of heating with ASHP worthwhile over a plug in electric heater?

Nope. We've 200mm, for comparison. Main reason being you're going to have the heating on a lot, lot more with UFH dut to the heatup time. If it's an occasional space, just heat when needed. 30mins with a 3kW blow heater will get it up to heat no bother. 

 

And for the brewing, I still use my insualted box with heat mat, even though the basement plant room is always 19-20c.

Edited August 27, 2023 by Conor

[Mr Ben]

10 minutes ago, Conor said:

Nope. We've 200mm, for comparison. Main reason being you're going to have the heating on a lot, lot more with UFH dut to the heatup time. If it's an occasional space, just heat when needed. 30mins with a 3kW blow heater will get it up to heat no bother. 

 

And for the brewing, I still use my insualted box with heat mat, even though the basement plant room is always 19-20c.

200mm is under your garage or house? It's not really an occasional space in terms of heating, but I'm not looking for house temperatures. Stable in the low teens through the winter would be ideal. 

[Mr Ben]

35 minutes ago, JohnMo said:

Or fan coil unit, for heat and cool. Make best of CoP and cooling ability.

This might be the way to go

[Mr Ben]

4 hours ago, SteamyTea said:

My concern is how much insulation is fitted under the floor.

If there is not enough, it could be costly to run an ASHP.

175mm of TLA in the house. Maybe less than I'd have liked if starting from scratch, but not awful? 

[Conor]

14 hours ago, Mr Ben said:

200mm is under your garage or house? It's not really an occasional space in terms of heating, but I'm not looking for house temperatures. Stable in the low teens through the winter would be ideal. 

 

Basement, technically part of the house but we don't hear it that much. Storage and plant.

 

13 hours ago, Mr Ben said:

175mm of TLA in the house. Maybe less than I'd have liked if starting from scratch, but not awful? 

 

Can't remember the figures bout about the same as 100mm PIR, so min to pass BC. It's not a simple as.that though, as the stuff doesn't have any joins or gaps so it'll perform better. We used in on on intermediate floors on top of the precast slabs.

 

 What's the garage floor build up again? XPS, then TLA, what goes on top? Structural screed or concrete? If you've 200mm build up to play with them I'd go 100mm PIR and 100mm concrete with UFH.

[Mr Ben]

14 hours ago, Conor said:

 

Basement, technically part of the house but we don't hear it that much. Storage and plant.

 

 

Can't remember the figures bout about the same as 100mm PIR, so min to pass BC. It's not a simple as.that though, as the stuff doesn't have any joins or gaps so it'll perform better. We used in on on intermediate floors on top of the precast slabs.

 

 What's the garage floor build up again? XPS, then TLA, what goes on top? Structural screed or concrete? If you've 200mm build up to play with them I'd go 100mm PIR and 100mm concrete with UFH.

Yea, this is where the problem lies. I'm limited to 130mm because of the requirement for 100mm drop from house FFL. 

 

XPS + 55mm screed + 5mm wearing layer is what's proposed. 

 

I'm thinking phenolic PIR has basically half the lambda value of XPS, but only 150kPa.

 

 

[Declan52]

43 minutes ago, Mr Ben said:

Yea, this is where the problem lies. I'm limited to 130mm because of the requirement for 100mm drop from house FFL. 

 

XPS + 55mm screed + 5mm wearing layer is what's proposed. 

 

I'm thinking phenolic PIR has basically half the lambda value of XPS, but only 150kPa.

 

 

I think with only 130mm to play with your going to have choose either heat or strength.

A 50mm screed with 80mm insulation will give you enough coverage of the ufh pipes but not enough strength to be lifting cars up. 80mm of insulation over a suspended floor ain't great for keeping the heat in.

I would just put concrete in at 130mm and live with the colder floor and look at beefing up the insulation in the walls and roof and garage door to try and keep it as warm as possible. 

Will this garage be an actual garage and have a car in it all the time or like most garages just end up a temp storage area for stuff to go to the dump.

 

[saveasteading]

To turn a garage into a man cave I would just insulate the floor. 25mm of pir o ee the slab and floor boards over. Your feet will feel warm, and that is the main issue. Then heating of yourself at your workstation by infra red

 

[Conor]

8 hours ago, Mr Ben said:

 

XPS + 55mm screed + 5mm wearing layer is what's proposed. 

 

 

 

Is the 55mm layer TLA? If that's the case then this buildup will be terrible. Even when set, the TLA is like a sponge. It's won't take any kind of point loading at all, and the 5mm SLC will crack.

 

What stage is the floor build at? Is it block and beam or precast concrete planks? If block and beam, you can lift the blocks and replace them with EPS.

 

Otherwise, I think ~80mm PIR and 50mm liquid screed is your best option.

[SteamyTea]

8 hours ago, saveasteading said:

Then heating of yourself at your workstation by infra red

Or an A2AHP.