Block Build & Air Tightness

T

trafficpat

Guest
Hi,
Were going standard block build ( 3500sqfoot) but would like to achieve air tightness. Were getting a MHRV system, underfloor heating off oil ( temp till we can afford different system ) and solar panels.
We have been hearing all sorts of stories, is there anyone that has an air tight house with block, was this easy to achieve, any tips?
Also we are looking for a stove? Whats teh best way of going about this?
Any input would be helpful.
Thanks
 
Hi trafficpat,
There are air-barrier membranes you can use to wrap the inner leaf with, or you can also use the vapour control membrane on the inside section of the wall construction as a measure to control air-leakage, a system they use in Canada is to spray a closed cell foam on the inner leaf which acts as insulation and air and vapour barrier, (must be closed cell) take your time and use the net for research, I hope this helps.
 
One of the most amusing things is the way Irish builders consistently decide to put vents into the rooms and just dig a big hole in the wall to the outside. Thus wasting a lot of the insulating effort that has gone into the house.

I suppose it is part of the hot press mentality, only in Ireland
 
An assessor in Loughrea lately told me it cost his client almost 5k to make his block build airtight. A HRV system will struggle to work properly in a house that is, essentially, porous.

Blockbuild is a poor choice in this modern age, with an eye to performance. It's only benefit is cost-to-fit, which will be long wiped out, down the road, in increased heating costs.
 
The block vs timber frame debate has been discussed in previous threads so Im not going to re-visit it except to say it is far too simplistic a view to state that block build is a poor choice. It is just as achievable to build an air tight energy efficient home in block as it is in timber frame if you plan it so from the start.

Traffic Pat my advise to you is before you build have an energy assessor complete specification improvement on your plans to assist you in reaching your required air tightness. aim for a result of 5m3 or under in an air tightness test & any property achieving 5 or under should def have a MHRV system.

And for what its worth in my opinion underfloor heating & oil is a big mistake. it will crucify you in cost.
Best of luck.
 
The reason were putting in Oil is because we cant afford Geothermal right now and we were told that Air to Water isnt that great ( Or is it? ) ? What system would you recommend putting in?
 
Im certainly not the expert so I cant really give you a definite answer on that. As you will see from another thread (titled home heating options ...please save me), I am at the very early stages in a self build & trying to decide on which heating system is the best for me. From my own experience I would recommend whichever system you plan on using to try & meet with people who have a similar system in a similar house (size & insulation etc) & talk to them. For my own part I met with two different people with underfloor & oil & their experience was that it was very expensive to run. One of them is in the process of changing to an air to water pump. Am looking in to this system myself & although I am far from convinced I plan to meet some people shortly who have it installed & get their experience. Of course there is a lot to be said for the more traditional oil & rads with a stove boiler as back up. I know you dont want to hear this but you could consider reducing the size of your house & installing a really efficient geo-thermal system. I dont know your personal circumstances but your house is massive ! This is coming from someone who is building a 2500 sq foot house & feels it is too big by about 500 sq foot. Hope that helps.
 
trafficpat,

There is no problem achieving air-tightness with a block build.It all comes down to attention to detail.The areas where you may have a problem are at door and window jambs - this is where the plaster meets the window/door frame.Again this is not difficult to get right.The ironic thing is that you are far more likely to get air leakage in an actual window or door seal - and this equally affects whether the house is block/TF/ICF etc.
If you think about it you have 2 leafs of blockwork with a cavity closer under your wall plate.Therefore your cavity has minimal air flow.On the cavity face of the inside leaf you will have your cavity insulation and the internal face of the inside leaf will be either plastered or dry-lined.You won't get air-flow thru your blockwork only at junctions of windows/doors & roof if not built properly.
The 3 areas you need to closely look at are:
- the house design - is the house orientated correctly to get the maximum free heat from the sun.Also are there any windows on the north face.If so keep them to a minimum and consider triple glazing them.
Your house is a big house and the one issue you may have with blockwork are expansion/contraction cracks.Check if there are any unusually long stretches of wall without breaks.The house may need expansion joints built into it.This is often forgotten and I think the reason that people are shying away form blockwork.
- construction - be clear of what you are doing before you start.Insulation is important.Definitely look at dry-lining the inside face of the inside block leaf and the ceilings to if finances permit.Ensure that your windows are A-rated, there are some v. good deals out there at the minute.When doing the deal for the windows make the air-tightness test around the windows a prerequisite for payment.Withhold say 30% until all windows & doors pass the air-tightness test.With your house air-tight your MHRV system should work fine.Always ask to visit an existing house with a MHRV system if you are using an contractor to install it.You may need to revisit your choice of heating system - I would not run ufh from an oil burner.I have not yet seen a geothermal system that is cheaper to run than oil.IMHO they are not finished evolving for the irish market.
- cost - do up all costs before starting.It can cost between 1/2 to 3/4 of the build cost to finish the house depending on your taste.

Enjoy it
Wex Dude
 
kemosabe said:
And for what its worth in my opinion underfloor heating & oil is a big mistake. it will crucify you in cost.
Best of luck.
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The thing to remember is that if you succeed in getting your house airtight, and super well insulated (a proper envelope of insulation, with no gaps. triple glazed windows, no chimneys, no thermal bridges etc, oil will not crucify you in cost

The fact is, you'll use so little oil, it wont cost much

The German Passivehaus standard (look it up in Wikipedia) tries to achieve a heating requirement of about 15kw/h of heating/cooling costs per sq meter per year (incl hot water).

15kw/sq meter is so little that even if you use electricity to heat your house, it'll cost very little.

The problem is to achieve the standard, it'll cost you money. I for one would love an opportunity to try. Remember having a stove will compromise the insulation integrity of your house and create a thermal bridge to the outside.
 
Obviously if you achieve an extremely air tight envelope no heating system will be expensive however in my humble opinion oil & underfloor are in a way a contradiction & there are more efficient combinations out there. Also I dont recall trafficpat saying he was aiming for a passive house ? He is aiming for an airtight house with underfloor heating & a stove. This is a mile away from a passive house.
 
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