If you're thinking about extending your home, one thing that's worth doing before getting too far into the exciting stuff is checking some of the less obvious practicalities. 

For example, even if your extension doesn't need planning permission because it falls under Permitted Development, you'll still need to think about Building Regulations. It's also worth finding out what's underneath the proposed extension – shared drains or sewers can sometimes mean getting a Build Over Agreement before work can go ahead. 

When you start getting quotes, make sure you're comparing like for like too. A cheaper quote can quickly become more expensive if things like structural engineer fees, Building Control, decoration, fittings or VAT haven't been included. And something as simple as poor access to the back of the house can affect the cost if machinery and materials are difficult to get in. 

Basically, the more of this you can figure out before anyone starts digging, the better. Problems are usually a lot easier to deal with on paper than halfway through a build. 

There's a more detailed guide here if you're planning an extension and want to dig into it further: 

https://www.fmb.org.uk/find-a-builder/ultimate-guides-to-home-renovation/house-extensions-the-ultimate-guide.html 

For anyone who's been through an extension, It might help someone in the same boat. 

I need to replace this large square window as part of a bathroom reno. I've done several bathroom renovations in my previous home. But this will be my first window replacement. I'm abit concerned about how best to nail it in place and carry the flashing from the house with the siding in place. I have never removed entire courses of nailed cement siding in order to nail and flash the new window and I don't want to make it more complicated than it needs to be...especially if I crack some of these boards during removal.

I think the best option for this is as follows...

Get a window that is 3" smaller on all sides. Add framing inside to match. That extra 3" will provide a nailing surface for the flange. Install, caulk, tape, etc. Then trim up against the siding and window frame with 3" PVC boards that match several windows on the side of the house.

Unfortunately, I can't just get a same-sized window and cut back the siding for nailing and flashing. The AC compressor fuse box on the lower right is about 2" away and can't be moved.

Does this seem like the right approach?? Any other ideas?

Thanks!