Which concrete blocks?

[Nickfromwales]

22 hours ago, Iceverge said:

Has anyone got examples of Dot and Dab blowerdoor tests(not gamed!)? Did anyone get below 2ACH ?

 

When it comes to passivhaus airtightness the build types I've seen to have achieved those levels are wet plaster, tapes membranes/boards in timberframe, ICF, SIPS. 

 

 

Two one offs were @Gone Wests Icynene TF and an archive building somewhere in England that used Passive purple paint. 

 

I haven't come across any dot and dab getting below 0.6ACH. 

Just got one to <0.2.

 

Nothing to do with dot and dab btw, as air gets in/out of way more places than through seemingly porous masonry walls. Aerobarrier supported, along with my guidance as principal consultant for the client, plus a lot of diligence and GAF, and the 1950's sack-o-shart was transformed into an accidental EnerPHit standard refurb (only better).

 

Two examples of homes done with PP, one where the builder (a stubborn northern Neandertal) sprayed the entire house in ignorance; 3.02ACH as-built final score, much to the clients disappointment. This was because, despite my best efforts to point out what he was missing, he failed in all of the then-available opportunities to seal up essential junctions etc during the construction phase, the places where it would then be impossible to seal up later on.

 

I try to mentor people on airtightness etc when we're on a project, but to some it just too much effort for them to deviate towards, others simply just can't comprehend where this attention needs to be focussed and how to implement measures to suit. Quite frustrating tbh, when I have to tell folk how to make their home more comfortable and energy efficient when they aren't really all that bothered as it involves time, car, and money.

 

Even harder a sale when you have to ask a client to convey this to a builder...... I keep trying but the road is mostly uphill, still!  

[Tony L]

15 hours ago, Gus Potter said:

A few comments: 

 

1/ Your cavity tray is only one course above finished ground. BC will and I will pull you up on that. 

 

2/ The insulation shown as a triangle just below the cavity tray is unbuildable as detailed . You are concentrating on the technicalities rather than balancing this with what is buildable,  the cost and how you are going to make sure that what you are paying for actually happens on site. Don't blame yourself.. as unless you do this as a day job and have a feeling of build cost there is no way of you knowing this. 

 

3/ You have a wide cavity. Why not thicken the perimeter insulation up to 100 or more thickness. Have a look at how MBC do an insulated raft slab and pinch their ideas. Then you can omit the Marmox block unless you want to spend money. You could be pragmatic and use the same money in a better way and in the round still achieve what you are looking to do. 

 

Thanks for your input @Gus Potter.  When I say, “I designed the house.”, I mean, I did all the planning permission drawings & passed these over to an architectural technician, together with some notes about materials & build method (the Thermoblocks were part of my spec’).  The AT has done the drawings my detail drawing was taken from, above.  I expected him to do a lot better than this.  Now I am spending hours & hours teaching him how to do his job properly so he can improve the drawings before they go to building control.

 

My intention was to have EPS beads filling the cavity, with these going all the way down to the trench blocks.  I imagined the EPS installer would drill through the inside leaf near the floor to fill the area below the tray.

 

If I don’t need a tray & I can have two separate DPCs that would seem to me to be a better solution.  This was suggested to me on an earlier thread, but I thought the 2 separate DPCs suggestion was just for below my windows.  If we can use 2 separate DPCs the whole way round the house, that would be great.

 

Are you sure omitting the Marmox blocks is a good idea?  This is going to mean all my walls will be sucking heat out of the house straight into the ground.  I can’t follow @Iceverge’s detail above (thanks for putting this up, @Iceverge) because I’m building my inner leaf off the top of the B&B, which has already been built.  Here’s a picture of it during construction.  As discussed here previously, the cowboy builder sat the B&B on trench blocks, instead of on dense blocks (which were on the drawing), so there’s no cavity beneath the level of the B&B, & although he put the beam ends on DPC, he then bridged the DPC with mortar - see below.  The bit on the right of the picture, with the light coloured slips, is where the air brick periscope feeds air into the B&B void.

 

[Tony L]

I have a very high water table, so I think this will likely make the ground colder than if the trench blocks were sat in dry ground.  My trench blocks are going to be almost permanently damp, & I note @Iceverge's point about Aircrete blocks having to be kept dry, which is another reason I can’t copy the @Iceverge detail.

 

I’d be grateful to hear comments on these two ideas, below.  Could I wrap the DMP around the outside of the bottom of the inner leaf construction, as shown in blue?

 

& sorry for the thread drift, @flanagaj.  I hope you find my problem interesting & helpful, as you consider your build.

 

 

 

 

[Tony L]

Aircrete version:

 

When I did a cost analysis some time ago, the Marmox Thermoblocks didn't seem too pricey, for the perceived benefit.  When I find time, I'll dig out my figures.