What is the preferred insulation or filler for gaps in window frames?

[Samara1]

What is the preferred insulation/filler for gaps in window frames on the inside & also outside? Is it required ?

Builder told will cover this gap with architraves (inside) and aluminium angle frames (outside) for all the windows but no fillings.

[JacobZ · Accepted solution]

Hi @Samara1,

Thank you for your question.

Looking at the image provided leads me to believe the framing is completed and the build is in the beginning of the "lockup" stage. At this stage of the build, the external cladding, roof, doors and windows will be installed to create a weatherproof shell. Once this stage is complete, the builder will then move onto the fixing and fit off stage where services such as electrical, plumbing and gas are roughed in. After the services are run, the insulation can be installed, and the walls closed in. This would be the stage where this gap is addressed.

Your builder will likely fill this gap with expanding foam or small strips of insulation once it is time to insulate the house. It is worth having a conversation with your builder to ensure this is done, but I imagine it will still be a while before they are up to this stage of the build.

Let me know if you require further clarification.

Jacob

[Samara1]

Great points. thanks.

Builder told will cover this gap with architraves (inside) and aluminium angle frames (outside) for all the windows but no fillings.

so Is it required to fill this gap with foam / batts or leave it. 

[JacobZ]

Hi @Samara1,

It is a requirement under the National Construction Code that this gap in the framing is there, however I don't believe it is required for this gap to be filled. 

If you are concerned that this is a thermal "weak point" in your home, you are perfectly within your rights to ask that it is filled with a suitable insulative material.

Let me know if you have other questions.

Jacob