More advice required: CAVITY U VALUES

[zappastix]

Hi

Oldun and others have given me advice before on achieving U values for cavity.

Because I have found a good deal on Ebay my wool slabs have changed.

I have tried to understand all the values and how to achieve/add up block
work and cavity fill, but honestly life's to short - I don't understand it.

I do not understand this site;

http://www.heidelbergcement.com/NR/...D41A94/0/Thermalite_sustainable_code_2011.pdf

Just to refresh memories - plans went through back in 2008;

Specs specified Crown DriTherm Cavity Slab 32 Ultimate (75mm thick)
ALONG WITH STANDARD 100MM LIGHTWEIGHT BLOCK and regular facing brick.

This is what Slab 32 Ultimate gives me;

DriTherm Cavity Slab 32 Ultimate (75mm thick) =

Thermal conductivity (W/mK) 0.032
Thermal resistance (m2K/W) 2.30

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

THIS IS WHAT I WANT TO USE NOW;

DriTherm Cavity Slab 37 Standard

Thermal conductivity (W/mK) 0.037
Thermal resistance (m2K/W) 2.00

+

Outer leaf - Regular facing bricks (Heather)

+

75mm cavity 'fully filled'
DriTherm Cavity Slab 37 Standard

+

Thermalite Blocks Turbo 2.9N/mm2 (0.11 lambda)
215mm high x 440mm length x 100mm wide

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Could someone tell me what the values added together
(between the ~~~~~~~~~) would be.

The minimum U value I have got to achieve (year 2008) is 0.32

With the above, will I achieve that
(I would prefer to better just the minimum)?

I promise I won't ask about this again.

Very confused - Stephen

 

[hotrod]

Specs specified Crown DriTherm Cavity Slab 32 Ultimate (75mm thick)
ALONG WITH STANDARD 100MM LIGHTWEIGHT BLOCK and regular facing brick.

This is what Slab 32 Ultimate gives me;

DriTherm Cavity Slab 32 Ultimate (75mm thick) =

Thermal conductivity (W/mK) 0.032
Thermal resistance (m2K/W) 2.30

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

THIS IS WHAT I WANT TO USE NOW;

DriTherm Cavity Slab 37 Standard

Thermal conductivity (W/mK) 0.037
Thermal resistance (m2K/W) 2.00

The lower the U value the better (i.e. the lower the thermal conductivity which means less heat loss).

You are proposing to substitute a product with a U Value of 0.032 with one that has a U Value of 0.037. This is an inferior product and will result in a worse (higher) U value. Why?

You haven't given internal finishes so no one can give you final values. You are also suggesting a 275mm cavity wall - is this right?

 

[freddiemercurystwin]

Jeez your threads are like pullin teeth! What are all of the finishes, what is the conductivity of the bricks you are proposing, it isn't on their website, you will need to find out. I'm pretty sure your proposal would comply but the bricks could be the stopper, in anycase if your BCO doubts it as is quite possible despite your pleas that some bloke off a forum said it'd be OK you will need to prove it. As has been mentioned before in your previous thread the only sure way to confirm the U value will be contacting Crown and asking for a U Value check, they'll send you an email with the calc to shove under the nose of Mr BCO. Its what any of us would do if we had any doubts and needed it confirming. Unless you pay for the U Value software yourself or get your calculator out and do it the old fashioned way but you're not gonna do either of those.

So,

Phone brick supplier and ask for thermal conductivity of brick.
Phone Crown and ask for U value check.
Bask in your glory!

Use one of these,

 

[freddiemercurystwin]

Well you have grasped one part: that is that I do not know the U Value of your wall: because you have not included all of the required information!

Your primitive understanding of how U value calcs are worked out speaks volumes. To my knowledge there are maybe one or two posters on the forum who possess the software necessary to work out your U Values. They would still need to know the full spec of the wall and the conductivity of your bricks though. Nobody can tell you unless you provide all the information required, why can you not grasp this simple information? A 5 minute phonecall could be made to the manufacturer to find out the brick spec and then a call to Crown to get the calc. This is what any professional who does not possess the software or the time to do the calc the old fashioned way (and nobody will bother to do that for you) would need to do to prove your spec achieves your desired U Value. Yet you're too lazy to do that yourself?

 

[zappastix]

Fredy just browsing and I came across this post;

//www.diynot.com/forums/viewtopic.php?t=214481

You seem to have the same answer for others - enough said, me thinks.

 

[Norcon]

What you've posted above will take you down to 0.32.
Adding inner and outer surface resistances and some plaster will take you too U = 0.30
So yes you will acheive what you want.

 

[Norcon]

Have you considered premium high performance Kingspan Kooltherm K8?
http://tinyurl.com/6xtk7tk

This will take you down to 0.19
1200 x 450mm x 75mm board is £11.51 including vat.

 

[theoldun]

Zippy, now you have had your teeth out, sounds like you are in a fighting mood. Just to make it worse, there is a bloke in the Shetland Islands selling Dritherm at £1.00 a pack. Suggest, hire rowing boat at Brighton. Pack a flask and corned beef sandwich, row down the Channel, turn left at Dover, then straight pull all the way, up the North Sea. When you pass Hull, halfway there. Mind the oil rigs.
It is no big deal to work out U values, Ks are pretty standard and you can get your Rs from Ks and Us from Rs. We ran a quick calc for 75mm Dritherm 37 and came up with a R value of 3.21m2kw, which gives you a U value of 0.31w/m2k We checked crowns calculations and they agreed with us, so it must be our lucky day.
We list below crowns design calculations all based on LBC heather, 75mm cavity and a block with a lambda value of 0.11
Dritherm 37 with 0.11 block = 0.31
Dritherm 34 with 0.11 block = 0.29 with 0.16 block = 0.31
Dritherm 32 with 0.11 block = 0.28 with 0.16 block = 0.30
All calculations based on internal finish of dot and dab skimmed plasterboard.
Have already given you a list of 0.11 blocks
0.16 blocks are Celcon Standard, Thermolite Shield, Topblock Toplite Standard, Durox Superblock 4, Topblock Superblock 4.
Reason you can get Standard 37 cheap, is that no one wants it now as it will not stand up to present U values with out additional internal insulation.
If you want better U Value consider opening up cavity to 100mm.
Bon voyage
oldun

This will take you down to 0.19
1200 x 450mm x 75mm board is £11.51 including vat.

With respect Norcon, you may not be quite right there, he only has a 75mm cavity to start of with.
oldun

 

[zappastix]

What can I say Oldun - Top Man, yet again.

I can now take out my gum shield, wipe away
the blood and spit and concentrate on your
most helpful reply.

Another big thank you, including the 37 tip.