Help with cost advise on initial rear extension options

[tim8383]

Hi, looking for some help obtaining very ball park budget costs comparisons for the rear extension we are planning.

We have developed a number of different options and was hoping for some experienced individuals to help advise on the estimate cost differences between them before we make a decision on which one to develop further.  Appreciate this is rather difficult and can vary depending on level of finishes etc., but only after very board brush figures. 

The attached image shows internal and external view of the extension with the various different types of roof. Looking for comparison between the following:
V1 - lean too with gable
V2 - Full gable
V3 - Flat roof
V4 - Full lean too

The extension is 9m (wide) x 5m (40m2).

 

Initially we have assumed the following with cheapest first:

1.  Flat roof or lean too

2.  full gable

3.  lean too with gable

 

Any ideas of what the estimate cost between them would be would be much appreciated.

Any questions please ask.

Thanks

[Mr Punter]

I don't know where in the country you are but I guess between £2,500 and £3,500 per metre plus VAT.

[Carrerahill]

52 minutes ago, tim8383 said:

Hi, looking for some help obtaining very ball park budget costs comparisons for the rear extension we are planning.

We have developed a number of different options and was hoping for some experienced individuals to help advise on the estimate cost differences between them before we make a decision on which one to develop further.  Appreciate this is rather difficult and can vary depending on level of finishes etc., but only after very board brush figures. 

The attached image shows internal and external view of the extension with the various different types of roof. Looking for comparison between the following:
V1 - lean too with gable
V2 - Full gable
V3 - Flat roof
V4 - Full lean too

The extension is 9m (wide) x 5m (40m2).

 

Initially we have assumed the following with cheapest first:

1.  Flat roof or lean too

2.  full gable

3.  lean too with gable

 

Any ideas of what the estimate cost between them would be would be much appreciated.

Any questions please ask.

Thanks

I think the issue with this request is that it is very time consuming. 

 

I've QSed 3-4 of my own builds now varying from extensions to loft conversions and garages and a couple for friends and family and to do it accurately (so far I have always been very close to final built cost) it takes a long time, you would need to provide full warrant drawings to know full spec's etc. In my build one of the single most costly things was insulation, but looking at your build it will be glazing. 

 

The best thing is to get your drawing package, it will need to be the building warrant to understand details, and start to break it down into blocks. Price up the walls, price per block/brick plus laid price, volumes of concrete, cost to prep and pour, get your glazing quote, roof area, get roof material cost. You will need to apply standard labour costs for your area unless you are closely in tune with labour costs. 

 

You will probably work out a figure that won't be that far off, always remember daft stuff like joist hangers and fixings, chemical anchors. 

 

Another option would be a small one man band QS or building surveyor etc. They may do this for a keen price and it will help you understand where you stand. 

 

 

[tim8383]

11 minutes ago, Carrerahill said:

I think the issue with this request is that it is very time consuming. 

 

I've QSed 3-4 of my own builds now varying from extensions to loft conversions and garages and a couple for friends and family and to do it accurately (so far I have always been very close to final built cost) it takes a long time, you would need to provide full warrant drawings to know full spec's etc. In my build one of the single most costly things was insulation, but looking at your build it will be glazing. 

 

The best thing is to get your drawing package, it will need to be the building warrant to understand details, and start to break it down into blocks. Price up the walls, price per block/brick plus laid price, volumes of concrete, cost to prep and pour, get your glazing quote, roof area, get roof material cost. You will need to apply standard labour costs for your area unless you are closely in tune with labour costs. 

 

You will probably work out a figure that won't be that far off, always remember daft stuff like joist hangers and fixings, chemical anchors. 

 

Another option would be a small one man band QS or building surveyor etc. They may do this for a keen price and it will help you understand where you stand. 

 

 

 

Appreciate getting an accurate idea of cost cannot be determined without a lot more information.  What we are trying to determine is very estimate cost between the various different roof types.

 

The cost to eaves will be similar in each scenario as all have 2no. bi fold doors, similar amount of stone walling and same number of roof lights etc.

 

The unknowns are the costs associated with the roof and roof structure for the various types.

 

We really like the gabled extension but if its significantly more than the lean too or flat roof then we would probably avoid it.

 

Ideally trying to avoid heading down one path to find out its far to expensive and then having to start design process again and potentially re-submit to planners.

 

thanks

 

[SimonD]

18 minutes ago, tim8383 said:

We really like the gabled extension but if its significantly more than the lean too or flat roof then we would probably avoid it.

 

Ideally trying to avoid heading down one path to find out its far to expensive and then having to start design process again and potentially re-submit to planners.

 

The flat and lean-to roofs are pretty easy, the gabled extension may or may not be. As you've illustrated the design, it has a fully vaulted design which really needs the input of a structural engineer first as there are various options as to how to tie the trusses - this will have most impact on the cost. You could use a steel or glulam frame which tie the trusses at the ridge, or you can use ridged or cable ties. Steel portal frame may be the cheapest option as it could be as little as a few grand, but as already mentioned above, it depends on the details.