uvalue - blocks

[pixiepoo]

We will soon be ordering our blocks for our extension. Spec says Thermalite Shield (to give overall uvalue of 0.20) and the building merchant has suggested the cheaper Plasmor Fibolite (giving overall value of 0.21)

Overall the Thermalites are £250 more expensive than the Fibolites, what I’m trying to work out is how important that extra 0.1 point of uvalue is worth paying the extra £250 for. Will it make a large difference to our property or is it negligible?

 

[AronSearle]

Pretty much an immeasurable difference.

 

[tony1851]

The 0.1 improvement of the Thermalite over the Fibolite will probably pay for itself in terms of heating saved in about 500 years, give or take a century

 

[pixiepoo]

Haha nuff said! I'll go with the cheaper option...

Thanks guys!

 

[theoldun]

We will soon be ordering our blocks for our extension. Spec says Thermalite Shield (to give overall uvalue of 0.20) and the building merchant has suggested the cheaper Plasmor Fibolite (giving overall value of 0.21)

Your builders merchant has no idea of what they are talking about;
Thermalite are made by the Heidelberg Group and have a Lambda (K value) of 0,15W/mK.
Fibolite are made by Plasmor and have a K value of 0.25W/mK.
In your post you mention U value W/m2K To arrive at a U value you first work out your R value from your K value and then your U value from your R value No block manufacturer gives a U value for their blocks. They only give a K value.
Of the top of our head both make of blocks, depending on what the external skin construcion is and the cavity width and what cavity fill you are using, will comply with L1B target U value of 0,28W/m2K.
However to confirm need outer skin construction, cavity width and cavity fill.
Regards oldun

 

[pixiepoo]

Hi theoldun

I used the online calculator on Celotex's website, putting all the info for our walls and the only difference using the plasmor blocks were 0.1 uvalue ( but they are £250 cheaper)

We have bricks outer, 50mm air gap, 70mm celotex, blocks, dot dab, plasterboard.

 

[jeds]

I agree. The difference in u value between Thermalite Shield and Fibolites is about 0.01 W/m²k.

Just to exercise the mind: 1 Watt = 1 Joule per second.

Therefore a wall with U-value of 0.24W/m²k will consume 0.24/1000*24 = 0.00576 kwh per day per metre squared per degree of temperature difference.
Assuming a wall area of 30m² - That’s about 0.173 kwh/day.

A wall with a u-value of 0.25 consumes 0.006 kwh per day per metre squared per degree of temperature difference.
For the same wall area that’s 0.18kwh/day.

So the difference between the two for a wall area of 30m² is about 2.5 kwh/year. If you heat by gas that’s about 2.5x13.5p = 34p per year.

Taking a £250 difference in cost that will be about 73 years to get you money back if you go with the Thermalites.

Of course there’s present day value and interest to take into account as well. If you take an interest rate of….

Oh, *******s to that.