U-Value calculations

[newhome]

Does anyone have a link to an idiot proof guide to help me understand my U-Value calculations, and what ‘Ok’ might look like please. I don’t have a passive house, so it won’t be super efficient, and some of the assumptions in mine aren’t quite right I believe as surely if I have MHRV it shouldn’t say ‘ventilation natural, fans 5’ ? It also doesn’t take the extension into account either. 

 

I really just would like to form view of how my house performs, and how I might be able to calculate a revised value. I doubt I can change anything at this stage. Many thanks! Summary of mine is below. 

 

 

[newhome]

@Ferdinand this is your fault as some of the things you said got me thinking more about it 

 

 

[Jeremy Harris]

I put together a heat loss calculation spreadsheet ages ago, really as a "what if?" tool to try and see what effect changing different aspects of the construction etc had on the overall heat loss.  It does mean putting in some basic data about the internal areas of outside walls, floor, ceiling (or roof), window and door areas, U values etc, but generally gives a reasonable estimate.  Others here have used it and found that it comes pretty close to reality, but it doesn't take account of any incidental heat gain, from occupants, appliances etc.  You can download it from here and have a play with it, it may or may not be helpful!: http://www.mayfly.eu/wp-content/uploads/2017/01/Fabric-and-ventilation-heat-loss-calculator-Master.xls

[newhome]

Thanks @JSHarris I will have a look. I’ve got most of the area data I think as I assume most is similar to the data in the original sheets. Just that some of it I think is wrong. 

 

 

[Ferdinand]

3 hours ago, newhome said:

@Ferdinand this is your fault as some of the things you said got me thinking more about it 

 

 

 

All the best things are my fault.

 

Except vodka.

[PeterW]

@newhome what’s the ground floor construction as that seems way off ...?!

[newhome]

47 minutes ago, PeterW said:

@newhome what’s the ground floor construction as that seems way off ...?!

 

Standard foundations, celotex under the UFH, then anhydrite screed, timber frame, ‘supawall’ and blocks and render. So this essentially, plus render on top of the blocks. 

 

 

 

 

[PeterW]

Do you know the thickness of the celotex..?

[newhome]

11 minutes ago, PeterW said:

Do you know the thickness of the celotex..?

 

Not sure. There is some in the garage I think. Will look tomorrow night. 

 

Here is a photo but it doesn’t give much away I think. 

 

Do you think it’s ‘off’ in an overly optimistic way or pessimistic? 

 

 

 

 

[SteamyTea]

Do you understand the basics of thermal insulation and how the different metrics work?

If not, I am sure one of use can knock up something to explain it pretty well.

I am a bit busy with a show this week, but if you are not in a terrible hurry, I may be able to say something about it next week, as long as I am reminded.

[newhome]

19 minutes ago, SteamyTea said:

Do you understand the basics of thermal insulation and how the different metrics work?

 

Not really and it would be great if you could write something up (in numpty language). Thank you! I did physics A level but have forgotten it all . 

 

[A_L]

1 hour ago, newhome said:

 

Do you think it’s ‘off’ in an overly optimistic way or pessimistic? 

 

 

If your 163m²    floor is anywhere near square it would only take 50mm of Celotex to get down to 0.28W/m².K

[newhome]

7 minutes ago, A_L said:

 

If your 163m²    floor is anywhere near square it would only take 50mm of Celotex to get down to 0.28W/m².K

 

Here is the floor plan that it’s based on, although the bit at the back is now ‘filled in’ as per the second drawing but the calcs didn’t include it as it was an add on. 

 

 

 

 

[Ferdinand]

10 hours ago, A_L said:

 

If your 163m²    floor is anywhere near square it would only take 50mm of Celotex to get down to 0.28W/m².K

 

These are the approx. required building regs u-values for floors from here:

http://great-home.co.uk/building-regulations-u-values-how-have-they-changed/

 

0.28 would have been OK (ie meets the regs) before 2010, which is probably the date of the @newhome your PP.

 

Ferdinand

 

Edited April 4, 2018 by Ferdinand

[newhome]

10 hours ago, Ferdinand said:

0.28 would have been OK (ie meets the regs) before 2010, which is probably the date of your PP.

 

Planning permission was 2005, building warrant 2006 (there was another house already built under the same PP and building warrant before we bought the plot). 

 

So how would things be done differently today for the floor? The foundations where already here and we just did what the UFH folk suggested re the ground floor. Couldn't work out how thick the Celotex was I couldn't find any. Thought there was some in the garage but that was Quintherm and we didn't use that for the floors. At a guess the Celotex was 50mm but can't tell for certain as the invoices are still at HMRC. 

 

[A_L]

29 minutes ago, newhome said:

 

Planning permission was 2005, building warrant 2006 (there was another house already built under the same PP and building warrant before we bought the plot). 

 

So how would things be done differently today for the floor?

 

A U value of 0.13Wm².K could be achieved (just) with 130mm of Celotex

[newhome]

3 minutes ago, A_L said:

 

A U value of 0.13Wm².K could be achieved (just) with 130mm of Celotex

 

OK thanks. The floor levels would have been wrong for 130mm so the timber frame would have to have been done differently I guess. Long time ago now tho (2009) and things change. 

 

[Ferdinand]

3 hours ago, newhome said:

 

OK thanks. The floor levels would have been wrong for 130mm so the timber frame would have to have been done differently I guess. Long time ago now tho (2009) and things change. 

 

 

Yep. pretty much.

 

I live in a chalet bungalow conversion done around the same time or a little later (2007 I think for PP) and have some similar issues, although some of ours (eg roof) seem to be done to a somewhat better standard than then Regs but nothing like BH ‘best practice’.

 

It would be a significant project to redo it all, and would be difficult to justify. 

 

Tis why we often recommend to spend money on the 'fabric first' and keep the posh kitchen and the dog-spa for later, if the budget is tight.

 

I keep coming across potential aspiring rental purchases where the cosmetics have been done but not the fabric, and it would be necessary to undo then redo to make it acceptable in the long term.

 

Ferdinand

 

Edited April 5, 2018 by Ferdinand