Hip to Gable loft conversion

[chicd4]

Does anyone know how to calculate the volume for a hip to gable roof conversion. extending the ridge by 4.5m the height is 3.2m and front of eaves to the centre line (under the apex) is also 4.5m.

 

[noseall]

planning may not let you alter from a hip to a gable.

^woody^ will know for sure.

 

[chicd4]

Hip to gable is allowed under permitted development. I need to know the calculation of the additional volume so as to remain within 45 cubic metres as that is what I have left of the original 70 cubic meters.

 

[Symptoms]

chic - it's 21.6 m3.

Think of your new gable end as a pyramid; volume of a pyramid = 1/3(area of base)(height) = 1/3A x H. OK, to get area of the base (the triangle formed by the gable) it's 1/2L x H = 4.5 x 3.2 = 14.4. So the volume of the pyramid = 1/3(area of base 14.4 divided by 3 )(height) = 4.8 x 4.5 = 21.6.

All sucked from 40 year old memory of trigonometry lessons.

 

[johnhough]

Does anyone know how to calculate the volume for a hip to gable roof conversion. extending the ridge by 4.5m the height is 3.2m and front of eaves to the centre line (under the apex) is also 4.5m.

Multiply the amount the ridge is extended by the height from the eaves (usually the top of the facia board) to the top of the ridge by the entire width (from the face of the eaves at the front to the face of the eaves at the rear of the building assuming it is a side Gable. I'm not sure why you are using a measurement from the front of the eaves to the apex centre line unless it is a half gable) Divide the total by 6. Planning uses a more sophisticated formula but this technique will give you a volume within 1.5%. All measurement taken externally

 

[Frank2010]

Can someone provide a definitive formula if one exists? I'm not saying that either of the two calculation methods are right or wrong btw.

1. Is there a universal formula councils and applicants should use to calculate volume for hip to gable conversions? If not, are there multiple ways of calculating a volume that would be acceptable to both sides or could be discussed on that basis?

2. Does the council's calculation method over rule any other method automatically? Does an applicant have to prove under their formula that the volume is correct?

3. How would you consider the eaves in the equation? Front & back remain in place and side (end of terrace) have been removed?

Thanks!

 

[johnhough]

Can someone provide a definitive formula if one exists? I'm not saying that either of the two calculation methods are right or wrong btw. Up to you which one you use. The divide by 6 rule gives you a calculation tolerance in your favour.

1. Is there a universal formula councils and applicants should use to calculate volume for hip to gable conversions? If not, are there multiple ways of calculating a volume that would be acceptable to both sides or could be discussed on that basis? Not Multiple but there are a few. Why bother. If your drawings are accurate & the altered area dimensioned the council will in most cases accept your submitted calculation.

2. Does the council's calculation method over rule any other method automatically? Does an applicant have to prove under their formula that the volume is correct? Not that I know of but it easier to accept their calculation as gospel ( unless they have made an obvious mistake ) Just design the area to fit into their requirements.

3. How would you consider the eaves in the equation? Front & back remain in place and side (end of terrace) have been removed? It's safest to measure facia to facia front to back. The council are interested in the overall external size.

Thanks!

 

[Frank2010]

Thanks John!
Your comments all make sense. However in our case the horse has already bolted with our application turned down as we are a fraction over 40 cu m under PD. To complicate matters the build stands and we have been asked to reduce so we cannot just alter plans.
So I'm currently trying to establish whether dimensions are accurate, the approach used to determine the volume is correct and whether generally there is anything we missed that could help us determine that we are within PD guidelines. I'm struggling in finding a definitive answer as to what method of calculation and points of measure should be taken.