Making rough cill watertight. Could Flashband work?

[giznorm]

Hi all,

I'm building a timber frame garden room at the moment and I'm just about ready to install the windows. I've wrapped the building in breathable membrane but it's now time to waterproof the rough cill and window opening.

I know that some people use tyvek flexiwrap, but a full roll of this is pretty expensive when I only have one window and one door (and I'm on a lockdown budget!). However, I have quite a large amount of Bostick Flashband left over from when I did a quick repair to a bay window roof.

Could I use the leftover Flashband to waterfproof the window opening before installing the upvc windows? Or if not, is there anything else I can use that more readily available and affordable than Flexiwrap?

Thanks everyone! I really appreciate any help you can give.

All the best.

 

[giznorm]

I'm leaving this post up just in case someone wants to chime in for someone else's benefit ... but I bit the bullet and bought FlexWrap. Now to tinker with the budget spreadsheet to make it work.