Insulating to Min Building Regs

[Ian]

I know that most people here are building homes that will far exceed the minimum standards required by Part L of the Building Regulations (Part L = conservation of fuel & power)

 

I finished my own build about a year ago - it's a small 2 bed holiday home on a remote site in N Wales and I decided to build it to just meet the minimum standards allowable in Part L and I thought it may be useful to give those of you who are exceeding Part L requirements an example of minimum compliance for comparison purposes.

 

It's a single storey timber frame and timber clad bungalow with a net internal area of 71 m2 and an internal heated volume of 234 m3 (we've exposed the pitch of the roof internally). It's a rectangular shape on plan as it's built along the contour of a 1:8 sloping site. (Small rectangular bungalows are about the worst shape for energy efficiency). It's heated by bulk LPG and a combi boiler. No PV or other renewables. Naturally ventilated with no MVHR.

 

These are my SAP figures:

 

EPC C71

[Edit to add EI Rating of B81]

Averaged (area weighted) 'U' values for walls, floor and roof of 0.15

Actual 'U' values are:

floor 0.1 (we have a ground bearing conc slab with Hive app controlled underfloor heating and 300mm of EPS under the concrete)

walls: 0.21 (minimum allowed in Welsh regs).

Roof: 0.13

Windows 3G 0.8

Air test actual figure of 3.7 m3/(h.m2) (no special tapes or air tightness layer)

 

Energy demand figures from the SAP calculation:

Heating demand 3400 kWh (this equals 47.9 kWh/sqM of internal area)

Hot water: 2290 kWh

Electric for pumps and fans: 120 kWh

Electric for lighting: 314 kWh (all LED)

Primary Energy Demand: 106.1 kWh/sqM/year

 

[Edit to add:

CO2 emissions: 1,596 kg/yr

CO2 emissions: 22.49 kg/m2]

 

 

The house is warm and draught free. The things I like most about it apart from the location and spectacular views are the open plan layout with tall 'cathedral' ceilings, the u/floor heating and the 3G windows.

 

I'd be very interested in seeing comparative figures for your own builds.

 

Ian

 

 

 

 

Edited February 15, 2018 by Ian

[IanR]

Floor, Roof, Windows and air tightness all appear to exceed Regs, or are the Welsh Regs more stringent than the English ones I'm familiar with. 

Edited February 15, 2018 by IanR

[Crofter]

Sounds great, and a similar concept to my own place but a bit bigger. As IanR says your u values look to be better than the BRegs minimum.

I thought that an air test figure of under 5 meant you needed MVHR? Or have I mis-remembered that?

[Ian]

3 minutes ago, IanR said:

Floor, Roof, Windows and air tightness all appear to exceed Regs, or are the Welsh Regs more stringent that the English ones I'm familiar with. 

Welsh Regs are now different from England for Part L and they have adopted more of a 'fabric first' approach.

 

The minimum backstop 'U' values for wall, roof and floor are more stringent however I think the end result is very similar

[Ian]

1 minute ago, Crofter said:

Sounds great, and a similar concept to my own place but a bit bigger. As IanR says your u values look to be better than the BRegs minimum.

I thought that an air test figure of under 5 meant you needed MVHR? Or have I mis-remembered that?

I've been watching progress on your build with great interest due to the similarities in size of build. Your recent photo of your finished bathroom is almost identical to ours.

[IanR]

2 minutes ago, Crofter said:

I thought that an air test figure of under 5 meant you needed MVHR? Or have I mis-remembered that?

 

I remembered it as 3. I know Airflow don't advise their MVHRs are used in properties with a figure of more than 5.

[Ian]

 

@IanR

here's the relevant minimum 'U' values in the Welsh Regs but as in England you can't get an overall pass by just using these minimum values

 

 

Edited February 16, 2018 by Ian

[Ian]

4 minutes ago, IanR said:

 

I remembered it as 3. I know Airflow don't advise their MVHRs are used in properties with a figure of more than 5.

Yes it's 3.

[ragg987]

13 minutes ago, Ian said:

Your recent photo of your finished bathroom is almost identical to ours.

There do seem to be a lot of similarities in the various builds on here. Ironic, really, are we losing our individuality, one of the drivers of a self-build? I suspect Grand Designs has crept into our subconscious...

[Ian]

3 minutes ago, ragg987 said:

There do seem to be a lot of similarities in the various builds on here. Ironic, really, are we losing our individuality, one of the drivers of a self-build? I suspect Grand Designs has crept into our subconscious...

I suspect that the reason that my bathroom is very similar to @Crofter is that they are both very small buildings so have small bathrooms. They both have a shower rather than a bath + a WC and WHB.

Edited February 15, 2018 by Ian

[Jeremy Harris]

This is all from our SAP report, and doesn't reflect some minor improvements made since completion.

 

130m² net internal floor area, 1 1/2 stories, internal volume 344m³.

 

6.25kWp PV array built in to ~South facing roof pitch

 

Heating, hot water etc all electric, with ASHP for heating and hot water pre-heat. 

Hot water heat loss 1.3 kWh/day (this was from SAP, when we had the thermal store, before we fitted the Sunamp PV, that reduced this to 0.6 kWh/day).

 

Average fabric U values:

 

Roof = 0.09 W/m².K

External Walls = 0.12 W/m².K

Floor = 0.1 W/m².K

Openings = 0.74 W/m².K (all 3G)

 

Air permeability:

 

Actual air test result = 1.22m³/m²/h @ 50 Pa

 

MVHR fitted with 83% Appendix Q efficiency

 

Energy demand from SAP:

 

Heating demand = 3319 kWh/year or 25.53 kWh/m²

Hot water demand = 1283.2 kWh/year (now reduced by ~300 kWh/year due to replacing the thermal store with the Sunamp PV)

Space heating fuel used = 1327.57 kWh/year  (10.2 kWh/m²/year, but this is way out, the real figure is less than half this even in really cold weather)

Hot water fuel used = 1283.19 kWh/year

Electricity for pumps and fans etc = 617.56 kWh/year

Electricity for lighting = 484.47 kWh/year

Total electricity demand = 3712.79 kWh/year = 28.56 kWh/m² (this is massively in error - PHPP gives 12 kWh/m², in practice the house uses close to this, around 1450 kWh/year (11.16 kWh/m²), ignoring the PV generation)

Electricity generated by PV = -5270 kWh/year

Primary energy "demand" = -35.05 kWh/m²/year

 

CO₂ emissions:

 

-868.31 kg/year

-6.69 kg/m²

 

SAP EPC Rating = A 107

 

EI Rating= A 107

 

 

 

 

[Nickfromwales]

49 minutes ago, ragg987 said:

There do seem to be a lot of similarities in the various builds on here. Ironic, really, are we losing our individuality, one of the drivers of a self-build? I suspect Grand Designs has crept into our subconscious...

They all look pretty damn fine to us mere mortals, i assure you .

 

[SteamyTea]

1 hour ago, Ian said:

Energy demand figures from the SAP calculation:

How does that compare to reality, is it close?

[MikeSharp01]

52 minutes ago, ragg987 said:

There do seem to be a lot of similarities in the various builds on here. Ironic, really, are we losing our individuality, one of the drivers of a self-build? I suspect Grand Designs has crept into our subconscious...

I suppose that in the end they are all just 'machines for living' in so no individuality there then but once you get into the details, site, house size, shape,  orientation, actual U values and so on it all gets very different and because people here are pushing the limits in many places the differences will increasingly small as the 'S' curve reaches its limit (carrying capacity) and we all be using the same technologies to achieve our 'individual' dream.

[Ian]

32 minutes ago, SteamyTea said:

How does that compare to reality, is it close?

with the building being a holiday home that is mainly used at weekends it's difficult to compare actual figures to the ones in the SAP.

 

We are into our second winter of heating now and a 1200 litre tank full of LPG (approx 8,400 kWh) is definitely going to last more than 2 years with the LPG being used for heating and all hot water (edit: and also cooking). The u/floor heating is on all year 24/7 at a minimum 'frost' setting of 12 degC and then I boost it to 19 degC via the Hive app if I know we are going to be there at the weekend. Once it's at the higher temperature for the weekend it then takes several days before it settles back to the frost setting of 12 degrees. In winter f it's at 19 degrees on a Saturday morning and 0 degrees outside temp and I then turn the thermostat back to 12 it would typically be Tuesday morning before the heating turned itself on again to the frost setting..

Edited February 15, 2018 by Ian

[Jeremy Harris]

57 minutes ago, SteamyTea said:

How does that compare to reality, is it close?

 

 

My experience has been that SAP massively over-estimated our energy demand, particularly the space heating requirement. 

 

SAP also puts a really daft COP figure on the ASHP, in reality were getting a COP of between 3.5 and 4, over 4 sometimes, whereas SAP seems to assume that the COP will only be 2.5.  This makes a pretty big difference to the primary energy figure, especially since SAP seems wholly unable to account for either the ASHP preheating the water or that most of the hot water comes from diverted PV energy. 

 

The net result is that the SAP primary energy consumption figure is massively in error, so much so as to be meaningless, really.

 

Equally meaningless is the way SAP just subtracts the PV generation from the total - it's crude and wholly non-representative, IMHO.  In fairness, I suppose SAP was never intended to be useful for a passive house, so perhaps being critical of these gross inaccuracies shouldn't really be blamed on the SAP methodology.

[Ian]

Gas Costs:

We have no mains gas where the holiday home is located so the main choices are bulk LPG or oil. I went for LPG as the location is very remote with no immediate neighbours and I didn't want to arrive there one weekend to find all the oil had been nicked. I did try to get Planning Permission for PV but was refused.

 

The guage on a bulk LPG tank is not a very precise way of measuring things but it's looking like we are using around 3,400 kWh of gas a year for heating, hot water and cooking(about 485 litres of LPG). The LPG cost was 30p per litre so that's an annual cost of £145 + the standing charge of £60. (At home where I have mains gas it costs 2.6p per kWh and 3,400 kWh would have been a cost of £88.40 which better puts things into context).

 

Electric Costs:

Our annual usage is 1,300 kWh.

 

I worked out that it's cheaper to be on a tariff with no standing charge but pay slightly more per kWh. At a rate of 16.2 p per kWh the total annual cost is £210 per year.

 

Water:

We have a metered mains supply with Welsh Water (who are brilliant btw!) but no mains drainage. (I have a Biopure 1 sewage treatment plant the same as @JSHarris )

Total water cost including standing charge is £50 per year

 

 

 

 

Edited February 15, 2018 by Ian

[Ian]

@JSHarris

Good point about the inaccuracies of SAP for low energy buildings.

 

The one that made me smile is the EPC where it makes recommendations for improving the energy performance of the building.

 

Here's the list which is supposed to be implemented in the same order as on the list:

 

 

 

Edited February 15, 2018 by Ian

[Jeremy Harris]

The EPC recommendations are hilarious, especially the pay back periods.  Here's a screenshot from ours:

 

 

It doesn't mention any band change presumably because we're already well above Band A.

 

If solar thermal cost £5k, then at £195 over three years it would take over 76 years just to recover the investment, not accounting for repairs, maintenance and replacement of out-of-life parts.....................

[Ian]

Here's a page from the NHBC's guidance in how to achieve minimum compliance with the Welsh Part L regs. They do examples for 5 differing types of house from mid terrace to large detached. Most forum users will know how the SAP calculation works but for those who don't the various elements in the suggestions in the table can be altered. For example you could decrease the thermal insulation of a wall as long as you increase the value of one of the other elements in the table.

 

Comparing my own build to this table it would have come under option 3 as I didn't have MVHR or renewables.

 

 

Edited February 16, 2018 by Ian

[gravelld]

On 15/02/2018 at 11:53, Ian said:

Air test actual figure of 3.7 m3/(h.m2)

 

Maybe I missed something, but in no way is this "just meet the minimum standards". It's going to make a massive difference to a developer box built to 10 m3/(h.m2) (and probably not achieving it).

[Ian]

@gravelld

yes, I think you’ve missed something: the 10 m3/hr/m2 figure is the absolute minimum backstop figure for airtightness in the Part L Approved Document. If you just met all the various backstop figures in Part L then you would have no chance of meeting the minimum overall standard.

 

SAP is effectively a complex spreadsheet where all the key building design inputs interact with each other to allow a flexible approach to design although there are also minimum backstop values that you need to meet for any single element.

Edited February 16, 2018 by Ian

[Jeremy Harris]

It's interesting looking at how the big developers are really good at building right down to minimum levels, yet still manage to get acceptable SAP results. 

 

One development that I've become fairly familiar with (largely because I drive past it every day) has utilised the ability to trade off one element against another in order to get an acceptable SAP result very cleverly.  One of the things they did was to add a few solar panels on some of the houses, often not at all well located (in one case on the north face of the roof).  The fabric standards for these houses weren't great, but they did use reasonably good doors and windows.  None have MVHR, as all have trickle vents in the windows.

 

I worked through some SAP rough estimates, based just on what I could see, so very much educated guesswork.  What seemed clear was that they were gaming the system.  Adding a few solar panels made a big difference to the SAP rating, even if those panels were unlikely to deliver their rated output, for example.  Similarly, using better than minimum standard windows and doors on the smaller houses compensated in part for just building the floors, walls and roof to the minimum standards.  Most had small (pretty impractical) draught lobbies that were probably exactly at the minimum floor area of 2m² tacked on the outside, again I suspect this was just to slightly improve the SAP rating.

 

My personal view is that although what's been done is compliant with the letter of the regulations (assuming the workmanship was OK, which from my observations it doesn't seem to be), in practice the houses are very unlikely to perform anywhere near as well as the SAP EPC suggests.   What's happening is that an illusion is being created that energy efficient new houses are being built, when the reality is that they probably aren't.

 

 

[gravelld]

On 16/02/2018 at 19:51, Ian said:

@gravelld

yes, I think you’ve missed something: the 10 m3/hr/m2 figure is the absolute minimum backstop figure for airtightness in the Part L Approved Document. If you just met all the various backstop figures in Part L then you would have no chance of meeting the minimum overall standard.

 

Sorry... what?

 

What overall standard?

 

Does the Welsh system have some overarching standard to achieve, rather than the individual items?

[Jeremy Harris]

1 hour ago, gravelld said:

 

Sorry... what?

 

What overall standard?

 

Does the Welsh system have some overarching standard to achieve, rather than the individual items?

 

The English standard is the same, if you just meet the minimum fabric standards in Part L1A then the chances are you won't get a "pass" in SAP.  It's one of the things that makes it essential to juggle all the various insulation level, airtightness level, fuel type, use of renewables etc around in order to make sure you get an acceptable outcome.