Topic: R Values

R Values 

I'm trying to understand the value of R values for my house.

If a double glazed window is below the required R values for cladding then wouldn't any heat loss from them mean the high value elsewhere would be negated?

Also - When a friend looked in their ceiling at the blown in insulation that was put in their house when new it had all turned to powder so it was totally ineffective and any heat would be going straight out the roof.

If double glazed glass is less than R1 then wouldn't a solid block house be good enough with a similar R value.

Also - what happens with thermal mass for warmth when there are endless gray days in winter with no sun?

And finally - because of the leaky building problem associated with so many monolithic polystyrene houses is polystyrene as an insulation material a problem when it comes to selling a house to the general public.

There seems to be problems with every material and every building technique.

Max

Re: R Values 

hi Max , heres my opinions on this

"If a double glazed window is below the required R values for cladding then wouldn't any heat loss from them mean the high value elsewhere would be negated?"

For the "overall" wall yes there is a negation of the R value, but you have to remember that the window is usually only a certain percentage of the wall. I believe there are various methods of calculating the building heat loss which allow you to trade of poor insulating elements such as windows with other elements such as say putting R5 batts in the roof for example.

Don't know about your mates house, never heard of an insulation turning to dust? It wasn't insulated with vermiculite was it, thats a loose fill mineral insulation.

R1 block house - no, again I think the minimum R values for walls are already making the assumption of low R value windows, therefore the compensating fudge factor is already allowed for.

On endless grey days the thermal mass will release its stored heat if it is warmer than the room temperature, once parity is reached the mass will cool at a rate which tracks the heat loss of the room.

"monolithic polystyrene houses" - I'm just in the process of building one with the Cornerstone ICF system, but I've clad it with weather board over a cavity, so I'm hoping there wont be problems when I come to sell. Not planning to sell for a good 15+ years though.

Pete

Re: R Values 

Thanks for the reply Pete.

I think the insulation was a type of shredded paper type product.

I guess with a cavity there wouldn't be a problem with any product and weatherboards wouldn't raise the concern that a lot of people I know have with plaster.

I've also heard today that concrete blocks crack and leak too so once again on the roundabout of products.

Thanks
Max

Re: R Values 

yeah, what Pete said re' insulation. You need to look at the whole beast. walls, windows, floor and ceiling.

With regard to cladding, if your worried about a leaky building remember 9/10th's of the battle is design and install. I reckon plaster over poly cladding (EIFS) is a very weather tight cladding...so long as the design of the building is not a shocker...and the tradesman that work on the building know what their doing,. flash it properly etc. According to the NZ building code, E2, EIFS cladding over a cavity can be used in the highest 'risk score' type of designs providing its designed and installed as per the details shown as an acceptable solution in that code. hope that makes sense.
Bottom line is don't dismiss a cladding type just because it's picked up a bad rap, unfairly, from being used on buildings of poor design and not being installed properly.

Re: R Values 

Hi Max,

Pete is right in what he says.

The insulation envelope in your house is no different to a sleeping bag. On a cold night what you are going to lose the most heat through is any holes (recessed downlights, slab edges, etc) and then any thin or lightly padded areas - your windows.

If you want to improve your comfort after filling the holes work with the thin areas first - double glaze, low E glass and more efficient window frames, good drapes.

Thermal mass is like a hot water bottle, it stores heat and lets it out only for as long as the temperature of the thermal mass is higher than the internal environment.

The difference is that with a house you don't boil a jug to fill the hottie (unless you out in a heating system), you use the sun to heat the thermal mass, hence the need for proper placement of the windows, and correct sizing and location of overhangs to prevent overheating summer. You don't want a hot water bottle in bed on a hot summer night.

On your other question of polystyrene clad houses what most people fail to understand is that there is no way that water can pass through the cladding system itself, all of the issues have been around penetrations through the cladding - windows, doors, pipes etc, and around the edges of the cladding.

Polystyrene systems are therefore no different to any other cladding type in having these vulnerable points. They were for a time especially during the late 90's commonly used for some much higher risk designs - no roof overhangs etc, which also corresponded with the era of deregulation which saw controls over building quality fall away shockingly and many of these buildings were built without even basic window and door flashings.

My impression is that the general public do associate polystyrene claddings with greater risk, but a well built poly clad building will be fine, and there is no cladding system that won't leak when poorly built.

The further away we get from the 1990's the less poly will play a part in peoples minds I think and the problem will be associated with a period in time rather than a specific cladding type - just my opinion.

Re: R Values 

Thanks for all the comments - that makes it a lot clearer for me

Max