I got questions... Dormer.

[RonnyRaygun]

Pencil, paper, and calculator...

 

[ibby]

Pencil, paper, and calculator...

I did that on page 2!

I dont know if I have calculated it right!
(have a look)

 

[RonnyRaygun]

Right, so your roof pitches front and back at around 36 ° , but from the side at 45 °

Ok, I reckon once you have put a gable on the end you will have added around 28 square metres. So if you drop your dormer roof around 0.7m from the ridge, you'll be able to make it about 6.4m long and stay within your 50m ² .

Very approximate of course...

Although just realised I worked it out on 60m ²
So actually your dormer can only be 4m long...
Maybe more balanced to have 2 dormers at 2m each, although you want a single one don't you?

 

[RonnyRaygun]

Your hip to gable will be about 23m³ to 25m³. That leaves, say, 25m³ for the rear dormer. Guessing about 4.2m deep x 3m high the maximum width of your dormer would be about 4m. (4.2x3.0/2x4 = 25.2m³) Which is a lot less than your sketch drawing. Bottom line is you can't build what you want within 50m³. You either need to compromise or submit an application.

I agree with jeds ...as I said I think your hip to gable is going to add something like 28m ², quite a bit more than the 19.2m ² that you worked out...
Why not do something like this

 

[ibby]

Right, so your roof pitches front and back at around 36 ° , but from the side at 45 °

Ok, I reckon once you have put a gable on the end you will have added around 28 square metres. So if you drop your dormer roof around 0.7m from the ridge, you'll be able to make it about 6.4m long and stay within your 50m ² .

Very approximate of course...

Although just realised I worked it out on 60m ²
So actually your dormer can only be 4m long...
Maybe more balanced to have 2 dormers at 2m each, although you want a single one don't you?

I want a single, so when the doors open you are straight into the highest part of the loft.


If I gave up space at the front of the house, and installed no windows and just used it as storage - would that give me more room at the back? How does the allowance work?

Can I use it as storage and board it out, but put no heating or windows in?

 

[ibby]

Why not do something like this

I thought about that,

because my architech never climed into the roof space and like an idiot i have already paid him

I measured up with my limited knowledge and figured out I may not have enough height to install full sized doors, to the two seprate rooms where the dormers will be.

 

[RonnyRaygun]

If I gave up space at the front of the house, and installed no windows and just used it as storage - would that give me more room at the back? How does the allowance work?

Can I use it as storage and board it out, but put no heating or windows in?

AFAIK the 50m ³ refers simply to the increase in roof space; it doesn't matter what that roof space is used for. I'm sue FMT or Jeds can confirm this...

 

[ibby]

i am going to go up tommrow again and lay wood on the joists and walk around.

will keep you posted

 

[freddiemercurystwin]

Right, so your roof pitches front and back at around 36 ° , but from the side at 45 °

Ok, I reckon once you have put a gable on the end you will have added around 28 square metres. So if you drop your dormer roof around 0.7m from the ridge, you'll be able to make it about 6.4m long and stay within your 50m ² .

Very approximate of course...

Angles are (given the dims provided) 34° & 42°, how did you work out your volumes RR? As when the angles are different it gets a little more complicated!

I roughly worked the volume of the additional volume of the hip to gable to be about 27m³ and the dormer to be about 22m³, so 49m³ in total.

But that is not completely accurate for the reasons mentioned (also not allowing for the thickness of the roof envelope).

In anycase it would be pretty easy to nip the dormer down a bit or retain a hip just a much smaller one maybe, to help with the volumes if after doing proper measurements and proper calcs it turned out to be over the limit.

 

[freddiemercurystwin]

The allowance is additional volume on top of what you have, it matters not what you use it for, habitable or otherwise.

 

[ibby]

Right, so your roof pitches front and back at around 36 ° , but from the side at 45 °

Ok, I reckon once you have put a gable on the end you will have added around 28 square metres. So if you drop your dormer roof around 0.7m from the ridge, you'll be able to make it about 6.4m long and stay within your 50m ² .

Very approximate of course...

Angles are (given the dims provided) 34° & 42°, how did you work out your volumes RR? As when the angles are different it gets a little more complicated!

I roughly worked the volume of the additional volume of the hip to gable to be about 27m³ and the dormer to be about 22m³, so 49m³ in total.

But that is not completely accurate for the reasons mentioned (also not allowing for the thickness of the roof envelope).

In anycase it would be pretty easy to nip the dormer down a bit or retain a hip just a much smaller one maybe, to help with the volumes if after doing proper measurements and proper calcs it turned out to be over the limit.

he made a mistake caculating it first.
His calculations were based on 60m3 and not 50m3 allowance for me.

 

[RonnyRaygun]

Angles are (given the dims provided) 34° & 42°, how did you work out your volumes RR? As when the angles are different it gets a little more complicated!
I roughly worked the volume of the additional volume of the hip to gable to be about 27m³ and the dormer to be about 22m³, so 49m³ in total.

See below...

Right, so your roof pitches front and back at around 36 ° , but from the side at 45 °

Ok, I reckon once you have put a gable on the end you will have added around 28 square metres. So if you drop your dormer roof around 0.7m from the ridge, you'll be able to make it about 6.4m long and stay within your 50m ² .

Very approximate of course...

Although just realised I worked it out on 60m ²
So actually your dormer can only be 4m long...
Maybe more balanced to have 2 dormers at 2m each, although you want a single one don't you?

I worked out my angles by adding on a bit to the height to allow for the depth of the joists/ridge board, hence the 36 and 45 degrees.

 

[ibby]

I have a question,



When the dormers calculations are done, some of the space is already existing in the roof.

How is that space handled? Is it included or excluded from the figure?

 

[ibby]

Untitled

• ibby
• 14 Feb 2012
• 1

Red being the dormer and purple marking the old space.

 

[freddiemercurystwin]

I only included the additional volume created by the dormer ie the hatched volume was excluded.

You may well find that when good dimensions are taken and accurate calculations carried out it is within the limit. Then again ....