National Building Code 2010 The amount of fenestration and section 9.36

[Myrtbnye]

I am working on the design of a house and the architect wants a large room (living, dining and kitchen about 900sqft). She wants the walls to have a window and door to wall ratio of about 60%. How will this affect the effective thermal resistance of the walls?

 

[cda]

Welcome

Buy good glazing?

Give it a day or two for answers

The architect does not have the answer??

 

[tmurray]

I'm assuming the building is a Part 9 building.

In regards to 9.36, there is no impact that you need to worry about in regards to the effective thermal resistance of the walls. There are some limited situations where it would, like for manufactured homes, but otherwise the windows just need to meet the U value or ER rating and the remainder of the wall just needs to meet the R value for above grade walls. The code in general assumes a window to wall ratio of %22, but that is for an entire cardinal direction, but there is no restriction on this on most buildings.

Now, outside of the code, how will this affect the overall thermal resistance of this building face? Severely. The required effective R value of a wall is 17.5. For windows and doors it is about 3.5. A mechanical engineer once told me a rule of thumb was if the windows and doors make up %10 of the wall, they will account for %50 of the heat loss through that assembly.

 

[Inspector Gadget]

I am working on the design of a house and the architect wants a large room (living, dining and kitchen about 900sqft). She wants the walls to have a window and door to wall ratio of about 60%. How will this affect the effective thermal resistance of the walls?

The other issue that *may* need to be addressed is if the house in in the Saint Andrews/St. Stephen area, where there are requirements for earthquake resistance. Even then, unless two storeys, 60 per cent windows is permissible in a wall required to be a braced wall band.