Calculating U-value of garden basement

[LadyBuilder]

I am not sure how to calculate the U-value of the roof of the basement part which is under the garden. The 1 m of soil on top must have some insulation effect. Does anyone know how to calculate that effect?

Edited December 20, 2017 by LadyBuilder

[Onoff]

Is this any good?

 

https://inspectapedia.com/insulation/R-Value_of_Soil.php

[Jeremy Harris]

My suggestion would be to do a normal U value calculation, taking the R values of all the layers, adding them together and them taking the inverse to get the U value.

[Ferdinand]

And you can assumptions about the ground temperature from perhaps 1m down.

 

I think a number of say 6C might be alright for calculating heat losses.

[Ian]

@LadyBuilder

There's a free U value calculator here http://www.changeplan.co.uk/u_value_calculator.php

It's easy to use and has a drop down list of common building materials although the list doesn't include soil. For the soil I'd use the data in the link that @Onoff gave you.

[LadyBuilder]

3 hours ago, Ian said:

There's a free U value calculator here http://www.changeplan.co.uk/u_value_calculator.php

 

Thanks! this is the one I use too, but i am really not sure how to add the data from the link @Onoff gave me...

[A_L]

1 hour ago, LadyBuilder said:

 

Thanks! this is the one I use too, but i am really not sure how to add the data from the link @Onoff gave me...

 

Just remember Onoff's link is in imperial units. To convert to SI units you need to divide the R values by 5.678

 

e.g. 0.125 Ft²hr.°F/Btu is 0.022 m²K/W (for 25.4mm) which gives a thermal conductivity of 1.16W/m.K, or about 40x that of conventional insulations.

 

it is normal practice to ignore the soil in the case of 'green roofs'

[LadyBuilder]

 

2 minutes ago, A_L said:

 

it is normal practice to ignore the soil in the case of 'green roofs'

 

I saw that but in green roofs you normally have between 70-150mm soil. My garden basement requirement is a minimum of 1000mm which should actually have some sort of impact

6 minutes ago, A_L said:

Just remember Onoff's link is in imperial units. To convert to SI units you need to divide the R values by 5.678

 

e.g. 0.125 Ft²hr.°F/Btu is 0.022 m²K/W (for 25.4mm) which gives a thermal conductivity of 1.16W/m.K, or about 40x that of conventional insulations.

Thanks!

[ProDave]

What is a "garden basement"?

 

You talk of 1000mm of soil?  Are you building a basement, then filling it with soil to have a garden down there? or have I had too much single malt tonight?

[LadyBuilder]

13 minutes ago, ProDave said:

You talk of 1000mm of soil?  Are you building a basement, then filling it with soil to have a garden down there? or have I had too much single malt tonight?

 

ha ha... not quite that. I am excavating the garden, putting a room, then backfilling the soil above the roof of the basement so that I still have the garden... like this

 

 

[SteamyTea]

I think the IET (the electrical people) use 2.5K.m.W^-1 for soil.  They tend to be conservative, so stick with that.  I think there is a table in the 17th about it.

And just remember that every time your plants get watered you get some extra losses.

And from an experiment I did several years ago (grass growing), the plants add nothing to the thermal properties.

 

 

Edited December 21, 2017 by SteamyTea

[ProDave]

The point with the basement, is you use the U values of the walls floor and roof, but to calculate heat loss you don't use outside temperature, you use ground temperature which will be pretty stable all year round, especially at the floor depth.