building insulation, best practice

joe mack

I'm planning a single storey extension at home. Standard 9 inch cavity block walls, like the rest of the house. I would like to insulate to a high standard, floor walls and ceiling. Any advice on current best practice for insulation ? What type, thicknesses etc. Thanks.

Viking House

We put 6 inches of insulation on the outside of a 9 inch cavity block house in Wicklow during the Summer and the effect is amazing. It completly eliminates cold bridging.

dixiefly

How do you put on outside insulation? Is it a special type of insulation & is the house the rendered again?

Viking House

Just glue it onto the wall like this and plaster over it with a special fibreglass mesh supported plaster.

Sparky78

Viking House wrote:

Just glue it onto the wall like this and plaster over it with a special fibreglass mesh supported plaster.

What would you estimate the U value of this system?

Viking House

The U-value on the Paroc website for 150mm Paroc FAS 3 glued onto a concrete block wall is 0.233.
Here is the link http://www.paroc.com/SPPS/BI_attachments/Design_Guidelines_renderedfacades.pdf
All Scandinavian U-values are made worse by 0.06 to allow for bad workmanship. This is called the Delta factor. To get a fair comparison with Irish U-values we need to subtract 0.060 from 0.233 giveing a U-value of 0.173. When we changed from 9 inch cavity blocks to 25cm Poroton blocks the U-values come close to 0.11.

Sparky78

How would the Poroton block system compare price wise per m/2 with insulated concrete form?Was thinking of building with this.Any opinions on ICF?

Viking House

ICF was used in Scandinavia over 40 years ago and is now used mostly in foundations. Petrochemical insulations being non breathable and low density don't hold onto heat for very long. You get the "caravan effect" where your caravan is like an oven an hour after the sun comes out. Paroc is wrapped around most dishwashers, it gives off a waft of heat 9 hours after you turn it on.

The other problem was internal water vapour getting into the ICF walls causing mould growth even when HRV was used. If moisture gets into the walls you need to allow it to escape or "sweat". I prefer breathable construction.

These four items are all equally important in my view when assesing the efficiency of your house.
U-value
Decrement Delay (explained above)
Airtightness
Eliminating cold bridges
Reducing the external surface areas

We import our materials from Poland so the costs for materials to build a Passive house comes to about €42-€47/ft2 but this is expected to increase by 15% next year.

mjffey

Viking,

I saw on your website that you use the external insulation also on older houses, but how does this work? Do you have to remove the existing plaster, and what about the roof and the window sils? Do they have to be replaced?

Viking House

I saw on your website that you use the external insulation also on older houses, but how does this work? First

Do you have to remove the existing plaster, Only if its loose.
What about the roof and the window cills? Do they have to be replaced?

We insulated over the window cills on a house in Sandyford and we removed the cills and put on dummy cills on a house in Kilcock. These houses had enough overhang in the roof but the wall insulation needs to meet up with the roof insulation so some work needs to be done to the soffet.

ollie30

how do you fix external waste pipes,down pipes etc. to the externaly insulated house?also i have concerns if lets say a car caught the corner of the wall and removed the render or rolled into the wall how does it stand up to these albeit ab-normal but very realistic abuses would the wall dinge badly? i am not running down the method infact i like it ,i just dont know much about the down sides to it.

Viking House

How do you fix external waste pipes,down pipes etc. to the externaly insulated house? We often bury the downpipes within the insulation and we also have special fittings to connect the downpipes externally.

Also I have concerns if lets say a car caught the corner of the wall and removed the render or rolled into the wall how does it stand up to these albeit ab-normal but very realistic abuses would the wall dinge badly?

The insulation is very flexible and will spring back into place with most minor impacts. Major impact is easy enough to repair except when there is structural damage.

I am not running down the method infact i like it ,I just dont know much about the down sides to it.

Sparky78

Viking is Paroc the same as any other Rock wool or does it have more benefits(eg better U value)?
How do you make your system Air tight for HRV?
What type of roof system do you use?
Sorry about all the questions. I also like the idea of your method.

Viking House

Viking is Paroc the same as any other Rock wool or does it have more benefits(eg better U value)? It doesn't have a better U-value but it is about double the weight (Paroc is 210kg/m3, Kingspan is 30kgs/m3 to give a comparison) which means it holds on to heat a lot longer reducing the temperature fluctuations in your house, it also is resistant to 1100 degrees in fire and if you imerse it in water it will not take it in.
The five equally important things for a Passive house are U-value, Decrement delay (density of the insulation), Airtightness, Elimination of cold bridges, Orientation.

How do you make your system Air tight for HRV? The internal plaster on the Poroton block makes the walls breathable and airtight and we use an Intello membrane or 9mm plywood on the inside of the roof for airtightness.

What type of roof system do you use? We use 60mm softboard on top of the rafters to improve the decrement delay and to increase the density of the insulation in the roof. We cross batten under the slates/tiles to allow the roof to breathe. We use a membrane internally for airtightness and to prevent internal moisture damaging the roof structure.

Sorry about all the questions. I also like the idea of your method.