Experience With CavityTherm wall insulation

Greenfish

I am considering constructing my new build using common aggregate block work with 150mm cavity and CavityTherm full fill insulation. This gives me the u-value I want without going for wider cavity etc. But wondering if anyone that has used this product would like to share there experiences, or has any tips for my brickie. He has never used CavityTherm before, but has a reputation for good work generally. Pictures of it on site would be great, rather than the pretty brochure images. How does this product work in the real world?

Caffrey78

I'm using 125mm in my Cavity. Like yourself, my builder never seen or used this before. If you get in touch with Xtratherm they should send a Technical fella out to discuss the product in greater detail.
I have two rows so far built, we only started yesterday!!
The biggest thing is to make sure that it is tight, properly butt jointed together and if the plastic sheet is cut it must be retaped with good waterproof tape. Use cavitytherm corners both internal and external to avoid poor butt joints based on trying to butt joint against a moulded rib on every sheet.
I'll post pictures later so you can take a look for yourself, can you share yours please.
What did you go for in the floors and walls as a matter of interest.

rockabaloo

Do you know how it compares in price with pumped beads?

Caffrey78

I imagine it would around twice the price of pumped beads.
There are pros and cons for both.
CavityTherm will give a much better u-value for it's thickness.
Pumped bead done properly would reduce drafts around your reveals.
Pumped bead will fill the bottom of the cavity and eliminate any drainage for the slightest ingress of moisture through the external leaf.
Have your cavity pumped during warm weather as the pva glue used to bond the bead will pump and react better than during cold temperatures.
You can check during the build how well the insulation is fitted using CTherm, whereas with bead it is much more difficult.
Builders don't like change so keep on top of even the slightest gaps at the start and make sure they do it properly, even if they don't appreciate it.

What stage are you at?

Greenfish

Hi Caffrey, would be great to see those pictures as it goes up! Have heard from someone else looking for example real on site use of CavityTherm, so it would be a help for more than just me. I will certainly share my experiences and pictures when we get that far.

We are just getting out the ground, trenches in but lots of sub-structure to build and other ground work to do. Still thinking out some of the construction details. Insulating in the cavity below damp course with EPS board, and in the floor above the slab with 125mm PIR. Above slab so the UFH does not take forever to respond, could have been 200mm EPS but thought we would save the 75mm of head room. The devil is getting all the details sorted, avoiding thermal bridging, being air tight. Always interested to share ideas.

Good luck!

Caffrey78

The pictures I have were taken at dark, I'll try get more this evening and post them. Don't take any notice of the taped vertical joints, this was a misunderstanding. They were told that if the HIPS sheet was cut it needed to be taped on the external side, and not with duct tape!!
The lads are building the external leaf up first so photos will be of the foil side and not the hips side.
It seems to take forever to get out of the ground, thankfully the walls are going much quicker and the weather couldn't be better for building.
I avoided UFH as the extra spend on geothermal etc was throwing my budget.

Greenfish

Thanks for the picture. A bit surprised to see things done that way around, would have expected the inner leaf to go up before a few runs ahead of the outer. That seems to be what the CavityTherm instructions suggest as well, or maybe even the complete inner leaf then do the insulation but that means working with all the wall ties sticking dangerously out. Not sure how you are going to get the any taping done on the HIPS side when a board is cut to fit the run. Are you using the pre-formed corner boards? Hope that it works out OK.

Know what you mean about ground source costs, so putting in UFH but driving it from a wood burner (got a good supply of wood) and thermal store. An air source heat pump could be fitted as a fall back if we are too cold after the first winter, but with a little luck all the insulation and air tightness will mean that we don't need it. Not sure how much I trust the calculations, so but we will see won't we.

What did the boards cost you, you can PM me if you like?

Caffrey78

The hips butt joint is taped and then slotted into the gap. The PIR foam & alu facer are both hydrophobic anyway so any ingress of moisture will be limited.

I've attached both the good and the bad.
The Good - The corner panels are very good once installed correctly.
The Bad - Running a wall tie down the joint, opening it up and not in the slot preformed for it makes no sense. This is being fixed today!!

Granted this is new to most builders but the way I look at it is, you build the cavity to suit the insulation and not the other way around.

beyondpassive

Looks tidy, but the cold bridging will uno all your hard work if you dont pay attention to it :-)

Your first blocks on the floor should be AAC blocks or Quinlite, otherwise you have a big thermal bridge. In a low energy thermally massive house, you should have underfloor, as the temperatures will be steady. Geothermal and underfloor are not the same. Underfloor will work well with any renewables based system such as Gas boiler and solar hybrid provided you have an accumulator.

Greenfish

The corner looks good, but what were they thinking with the wall tie? Good reminder of what can happen on site (with a new product), keep the pictures coming as you progress.

Did some modelling on having a course of thermal blocks as Beyondpassive describes. If you have not done that (and the blocks all look the same to me) then don't despair, the impact of not having them may not be all that great. In a solid ground bearing slab it is less impact than in a suspended floor (B & with a vented void underneath. The more important thing is to take the insulation well down the cavity, or even insulate below DPC with something else.

Baltrasna2013

If you are installing wall ties at 225mm centres at openings how do you install wall ties in board. Do you need to cut a 150mm slot in the 450mm high board . Is there another way?

Caffrey78

Hey Baltrasna2013,

I'm struggling to understand your question.
Wall ties rest on the blocks top face and this lines up with the top of a CT sheet. why would you need to cut a 150mm slot down the board?

Carbonnet

Baltrasna2013 wrote: »

If you are installing wall ties at 225mm centres at openings how do you install wall ties in board. Do you need to cut a 150mm slot in the 450mm high board . Is there another way?

Double up wall ties at 450c/s - it's in the brochure.

CelicaGT

I was just looking at this product and I see that it does not have NSAI approval so I was wondering does this product comply with the building regulations?

Caffrey78

I'm building in Northern Ireland so the BBA certs cover my build.

Sligoronan

Just in the process of building and a house for a client. Find to hard to see me useing cavity therm again. Works out crazy expensive. When dealing with a lot of gables huge amount of waste. Also damp details need huge amount of care taken. Would sleep better at night if I had left it out and used a 200 pumped cavity with cosy board on inside. Think I paid 21 plus vat and on story and half pluse wast it has cost more than 30 plus vat per sq meter.
Hope I am wrong.

romeonovember

any idea what cavity therm costs per m2? I am looking at it for my 150mm full fill cavity. I am trying to get my wall design finalised so that I can get the provisional BER done.
thanks,

Shelly2013

romeonovember wrote: »

any idea what cavity therm costs per m2? I am looking at it for my 150mm full fill cavity. I am trying to get my wall design finalised so that I can get the provisional BER done.
thanks,

Hi romeonovember,
Did you get an idea of the cost of these thinking of going for the 150mm full fill myself?!

Carbonnet

Shelly2013 wrote: »

Hi romeonovember,
Did you get an idea of the cost of these thinking of going for the 150mm full fill myself?!

From the Cavitytherm web site

http://cavitytherm.com/wp-content/themes/cavitytherm/downloads/Cyril-Sweett-Report.pdf

romeonovember

hi shelly2013,

not going for the cavity therm now, but am going for a 250mm cavity full fill with platinum bonded bead. from discussing it with my engineer and architect I find its the best solution for my house.

brianwake

Hello romeonovember.

How did your 250mm cavity full fill workout?
Are you happy with your choice? would you do the same again?