Help with planning a house extension

[griffta]

Hello,

I'm seeking advice on building a reasonably large extension at the back of our house. Any guidance on evaluating quotes at each stage would be greatly appreciated. Our house is a three-bedroom brick construction from 1936. The land slopes from right to left when viewing the back of the house. On the left side is a basement with enough headroom for a person to walk in, while the right side has a conservatory supported by a brick structure to accommodate the slope. Attached is a photo for reference, which shows a raised decking area to the left of the conservatory where the basement access door is located.

We plan to replace the decking and conservatory with a two-story brick extension. The upper floor will be level with the house's ground floor, and the lower floor will require excavation on the right side and some excavation on the left. This extension will provide an extended kitchen upstairs and a garden room with bi-fold doors downstairs.

After obtaining planning permission with the help of an architect, we are now in the process of appointing a structural engineer through the architect. We have received quotes ranging from £1500 to over £5000, and some of them require a GIS survey. As we are new to this type of project, we would appreciate guidance on comparing structural engineers and determining the necessity of a GIS survey. We are happy to conduct research, but we wanted to ensure that our project approach is correct. Additionally, we are considering whether appointing a project manager at this stage would be advisable. If so, we would like to know what levels of project management are available and how they are costed.

Any help would be greatly appreciated!

Matt.

 

[oldbutnotdead]

So. You've decided what you want without even a guess at total project budget?
Yes you need a project manager last month, most extensions don't need an architect so that would have been your first saving.

EDIT You can't go design and build cos you've already got a design.
So you need either PM or a principal contractor who is willing and able to take that role on.

 

[freddiemercurystwin]

This is the kind of project that absolutely needs a good set of detailed Building Regs drawings and beyond, that should ensure you get like for like quotes and then they can form the basis of the contract documents, note these are quite different to your planning application drawings which only show the scope of what's involved. Ensure you're designer, be that an architect or anyone else suitably qualified works with the engineer to find a sensible and simple approach to the basement walls which if their design is OTT will frighten off many good builders who will can just stick to simple above ground stuff or will stick in an OTT price for the hassle. It doesn't need a PM at all if the builder is OK, I've never done a domestic extension where the SE required an GIS survey. You'll need deep foundations and even deeper pockets.

 

[mrrusty]

You can't go design and build cos you've already got a design.

I don't agree - it is quite normal (in the commercial world) to work up an initial design and then go out to tender on a D&B contract. The advantage of D&B is that you will have a fixed price. Disadvantage is you will pay for the contractors risk. May well be a price worth paying on a tricky build, rather than have the risk spread around.

Your architect may even agree to be novated to your chosen contractor. https://www.designingbuildings.co.uk/wiki/Novation

 

[robinbanks]

.

 

[freddiemercurystwin]

I don't agree - it is quite normal (in the commercial world) to work up an initial design and then go out to tender on a D&B contract. The advantage of D&B is that you will have a fixed price. Disadvantage is you will pay for the contractors risk. May well be a price worth paying on a tricky build, rather than have the risk spread around.

Your architect may even agree to be novated to your chosen contractor. https://www.designingbuildings.co.uk/wiki/Novation

You would never do D&B on a domestic extension. Ridiculous.

 

[mrrusty]

You would never do D&B on a domestic extension. Ridiculous.

Really? The last two extensions I have done have both been D&B. Gave the builder an outline specification and left it to him to sort out how he wanted to build it and look after ensuring regs compliance. Both done on building notices.

 

[^woody^]

we are now in the process of appointing a structural engineer

Why?

Normally, the client would not directly appoint an engineer, but the engineer should be appointed by the designer. There are liability issues for the designer's design and the engineers design.