Cost: Single Storey VS 1.5 Storey

bemak

I'm currently working up a design for a 4-bed single storey house for a friend of mine. The house is 140sqm (regular rectangular plan) but I think there is an opportunity to move 2-bedrooms up to the first floor and create a storey-and-a-half style house. (planning considerations aside)

My question is, which scenario is likely to be more cost-effective?

Option 1 - 140sqm (GF)
Option 2 - 100sqm (GF) with two bedrooms in roof space.

The way I look at it, Option 2 has a reduced footprint and as such, less slab and wall area. However, there would be additional cost in the roof structure to allow for the additional accommodation.

Just curious to hear people's thoughts.

jmBuildExt

Surely option 2! .... no expert though!
Added benefit that it should be cheaper to heat too..

bemak

I'm no cost expert but I'm not sure I'd agree re:heading. Option 2 will have more floor area when you include the attic space and this is area that needs to be heated. In Option 1 you could have 300-500mm of insulation above the ceiling to restrict the volume being heated.

jmBuildExt

Yeah i thought about it again after i posted... Maybe with modern standards re insulation, the old "heat rises" argument for 2 storeys being better than one, probably doesnt apply as much.
But id still say 2 is marginally better than 1 in this regard, but prob only negligable.

bemak

There's bound to be additional cost in the roof as well to allow for the main space to be free of structure.

Lumen

The nicest bungalows have vaulted ceilings. Can't do that with a storey and a half.

Which doesn't really address the cost question, but a fundamentally nicer structure beats money spent on finishes.

BryanF

Is this a self build or contractor build ?
Is owner willing to spend on dormer air-tightness /insulation design, or would simple envelope single storey ‘box’ be the ‘easiest’ to get right?

gooner99

I'm no expert at all, so may be way off the mark here.

The old thinking would seem to be to go 1.5 or 2 as the foundations, block work, roof areas would be smaller. But I guess Today there is much more expense in insulation and airtightness, heating systems, etc. So to this end I guess a 1.5 may have more insulation in the roof, heavier timbers, more trickier airtightness detailing, velux or dormers, underfloor to upper floor, stairs, extra bathroom. Probably other things I've forgotten.

Of course there may be extra costs with a single story that I've not thought off.

These are just a few tips I've read previously. I'm sure there are plenty other design and build money saving tips. If any of you have others it would be great if you could share them.

1. Keep the shape simple, rectangular box if possible. keep the size compact by smart use of space, open plan, minimal halls, porches, circulation areas.

2. Keep plumbing runs short, so try to keep kitchen, utility, bathrooms in the same area if possible and upstairs bathroom in that same area.

3. Not sure how this one works out, someone else may know better, but it goes like this...... Make sure all rooms are divisible by 1200mm x 2400mm. All sheet material comes in this size and you will incur significant wastage in materials if you don't. - Timber sheets, Insulation, Tiles, Floor coverings etc etc

bemak

BryanF wrote:

Is this a self build or contractor build ? Is owner willing to spend on dormer air-tightness /insulation design, or would simple envelope single storey ‘box’ be the ‘easiest’ to get right?

Will be contractor build. That's a very valid argument re: air tightness etc. I would imagine its a lot tougher to achieve in a dormer

MicktheMan

bemak wrote: »

Will be contractor build. That's a very valid argument re: air tightness etc. I would imagine its a lot tougher to achieve in a dormer

You're not wrong

severeoversteer

go full 2 storey or bungalow
storey and a half is very expensive to insulate and hard to airtight
insulating between rafters is far more expensive than using loft roll in a flat attic

Lumen

Obvs the shorter a building is the greater the volume to surface area, and therefore it's going to be more expensive purely on account of geometry, but I'd have thought it was simpler to achieve good airtightness and insulation in a modern build with external insulation and warm roof, in which case a bungalow or dormer is no different than two stories.