Loft Volume Allowance

[ChloeRadshaw1]

I managed to get hold of some plans which my neighbour had drawn up - Interestingly he did not get a lawful development and proceeded to build it

I want to copy him as he has done two hip to gables and a full width rear dormer but i do not understand how he and the architect which has indemnity insurance has suggested this would be <50 cubic metre

Can someone help me out here. I was told previously to obtain a plan when i asked this question so i ve attached what i have

The width of house is 10M, the depth of house is 10M and the existing roof height is 4.1M

Using this https://www.planningportal.co.uk/info/200215/volume_calculator_pitched_roof_two_end_hips
H = 6 (but i m not sure as I have not checked and i dont see why that would be needed! But lets assume that)
W=10
L=10
A=4.1
B=5
C=0

I ll send the helpful poster a bottle of wine!!!

 

[tony1851]

That is a lot more than 50m³ and would not be permitted development. Can I have my bottle of wine now?

 

[ChloeRadshaw1]

That is a lot more than 50m³ and would not be permitted development. Can I have my bottle of wine now?

Did you check the plans attached to the original post? They were drawn up by an architect on a house two doors down and he makes clear it is less then 50 cubic metres.

Did he make a mistake and therefore his indemnity insurance will pay up or have you made a mistake.

The wine will probably go to woody or someone else who can help answer the above and explain the volume addition by adding two hip to gables and a rear dormer

 

[freddiemercurystwin]

There you go Tony, woody is the oracle, FFS.

 

[tony1851]

OK Chloe, (and FMT), here goes.
Look at the two hip-to-gables first - they form pyramids. The volume of a pyramid is 1/3 the base area x the height.
In this case, one third of the base area of one gable, = 10 x 4.1 divided by 2 divided by 3 = 6.8m². The height is the distance along the ridge up to the existing ridge, which looks to be about 4.5m, so the volume of one hip-to-gable is 6.8 x 4.5 = 30.6m³. The volume of two hip-to-gables is therefore 61.2m³.
And this is before we add the volume of the flat roof dormer on the back, which you can jolly well work out yourself.
Now, about that bottle of wine.................

 

[freddiemercurystwin]

No I'd want woody to confirm I'm afraid.

 

[tony1851]

I managed to get hold of some plans which my neighbour had drawn up - Interestingly he did not get a lawful development and proceeded to build it

I want to copy him as he has done two hip to gables and a full width rear dormer but i do not understand how he and the architect which has indemnity insurance has suggested this would be <50 cubic metre

Can someone help me out here. I was told previously to obtain a plan when i asked this question so i ve attached what i have

The width of house is 10M, the depth of house is 10M and the existing roof height is 4.1M

Using this https://www.planningportal.co.uk/info/200215/volume_calculator_pitched_roof_two_end_hips
H = 6 (but i m not sure as I have not checked and i dont see why that would be needed! But lets assume that)
W=10
L=10
A=4.1
B=5
C=0

I ll send the helpful poster a bottle of wine!!!

Looking at the proposed plan, I would say that C is a little more than 1m, and B is around 4.5m.

 

[tony1851]

I'm still waiting for my wine.....................

Seriously, if the architect maintains that the total volume of that roof enlargement is < 50m³, there is something very wrong somewhere.

 

[ChloeRadshaw1]

OK Chloe, (and FMT), here goes.
Look at the two hip-to-gables first - they form pyramids. The volume of a pyramid is 1/3 the base area x the height.
In this case, one third of the base area of one gable, = 10 x 4.1 divided by 2 divided by 3 = 6.8m². The height is the distance along the ridge up to the existing ridge, which looks to be about 4.5m, so the volume of one hip-to-gable is 6.8 x 4.5 = 30.6m³. The volume of two hip-to-gables is therefore 61.2m³.
And this is before we add the volume of the flat roof dormer on the back, which you can jolly well work out yourself.
Now, about that bottle of wine.................

Very helpful - Thanks - I really wonder how the architect wrote down 50 cubic metres in that case

Just for my curiousity what would you say the rear dormer would add exactly in cubic metres?

Thanks very much

 

[garyo]

I'll throw the architect a bone and say that he may have created a good chunk of inaccessible attic space in front of those front dormers... Whether that would get it under 50m3 though?

 

[garyo]

I'm talking rubbish and thinking of floor area enlargement percentages As you were!

 

[tony1851]

what would you say the rear dormer would add exactly in cubic metres?

Please - it's gone half past ten at night!!!!!!!!!!

 

[ChloeRadshaw1]

I'll throw the architect a bone and say that he may have created a good chunk of inaccessible attic space in front of those front dormers... Whether that would get it under 50m3 though?

Is that how its done then? Create a massive dormer but block it off and say its not used to magically come in to < 50 cubic metre??!

 

[Nakajo]

The hip to gable is 45m3 (gross external volume) and the rear dormer is 48m3. So physics must work a bit differently up that way.

 

[garyo]

Is that how its done then? Create a massive dormer but block it off and say its not used to magically come in to < 50 cubic metre??!

No not in your circumstances I was thinking about the typical greenbelt over-development percentages where floor area is used (and can be manipulated somewhat by reducing the usable floor area)