loft conversion vs building over garage help

[tentative3]

In the process of buying a 4 bed detached. All the bedrooms are pretty small, as is the bathroom. There is a garage attached to the property and on the other side of the house a single storey extension with a pitched roof. The plans for the extension show foundations too shallow to allow us to build on top. We assume the garage foundations are too shallow as well. We would like to add a master suite and are debating the merits/costs of knocking down and rebuilding garage with a utility at the rear and a master suite above vs converting the loft and adding a single storey utility at the rear of the garage.

Does anyone have any views on the desirability of loft conversion vs first floor master suite? We assume the former will be substantially cheaper although we will want to do the utility as well. Would you rather buy a two storey house than one with a loft conversion? How much price difference would you expect?

There is a radical alternative which is to sacrifice a bedroom. Not sure on the impact on value.

Bit of a ramble really but would love any views or cost info!

Just because an extension has been done with shallow foundations, don't assume the garage has shallow ones too. It might have been easier for the original builders to do everything to the same depth.

We have done both - built over a garage and a loft conversion.
Building over garage is probably better imo as you get full height and fewer stairs.

It is difficult to judge with a loft conversion quite how much head height you will get (and they keep tightening up on insulation requirements). However somehow we have more usable storage now the loft is converted than we did before. I love our loft conversion, though it was a lot of money! (we did put in 11 windows).

Thanks for the response! Yes, I've seen mention before that sometimes builders just poured one lot of foundations for the house and garage. We'll have to hope but was your garage single skin?

Also, might I be cheeky and ask the approx cost of your loft conversion? We would want plenty of windows and a high end finish which is making me wonder whether the cost difference will end up being more marginal...

Our loft was around 60k all in around 5 or 6 years ago (South East).

This included removal of existing hot water tank and water header tank and installation of new fancy mains pressure water tank (magna something). 1 bedroom and ensuite with bath and over-shower, carpets, decorations, 11 windows. Fitted cupboards to end wall, storage area at top of stairs.

The amount of windows plus a slightly fancy bath pushed the price up.

Get an architect and Structural Engineer in for some advice.

You can underpin the garage and build what you want over it if that gives you what you need.

Are there other houses nearby that have done a lift conversion? I was really helped by seeing 2 houses that had done variants of what we had in minds. I didn't really know the owners but both sweet happy to show me around.

I'm not aware of any loft conversions but I'll have a look around.

We do plan to discuss with an architect and would need a structural engineer anyway for the work we intend to do opening up the downstairs layout. We're just itching to get on with thinking about what we want I suppose, and are undecided between the three options. If we had the garage underpinned what would that mean in terms of selling the property on (not that we have any plans)? Would it have all the undesirability of properties that have been underpinned due to subsidence?

We're going round in circles to be quite honest. Occasionally we arrive back at the idea that we should just reconfigure the space to three beds. It would certainly be cheaper!