Thanks
From the top of the wall plate i have 16 bricks to the underside of the upstairs bedroom window sill. BC inspector says he wants at least 2 bricks visible under the window after roof tils are on.
Hope this helps you.
thanks again
lean to roof
- Thread starter nottsrob184
- Start date
Thanks
From the top of the wall plate i have 16 bricks to the underside of the upstairs bedroom window sill. BC inspector says he wants at least 2 bricks visible under the window after roof tils are on.
Hope this helps you.
thanks again
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Okay. Joists. Depth of building is 12ft= 3660 less 300 width of cavity wall leaves you inside span, wall to wall of 3360. Joists required C16 50x175 at 400 centres.
Binders. Length of building 25ft = 7260 less two external skins and two cavities = 400 = 6860 overall span. Now you are bu**ered unless you have a centre internal load bearing wall from back of existing house to new extension back wall to sit binders on. Let me know, is it one room, or split in two?
Pitch. Depth of building 3660 less face wall and cavity 200 = 3460, therefore back of wall plate to existing house = half span of 3460.
Window is 16 course to under sill from top of plate = 1200 less 225 to allow for 150 lead flashing and 75 for batten and tile girth = rise of 975. Therefore 3460 half span and 975 rise gives hypotenuse of 3594 and pitch of 15.74 degrees.
However this is not the pitch of the finished roof as you now have to take into consideration the height of the rafter above plate. This is called HAP. Before going any further, lets look at rafter size. As it is uneconomical to use rafters deeper than 150 the tables only go up to 150 depth and then you start using purlins. You can go 3520 on a 50x150 rafter without using a purlin, but as you will be outside this measure, you could possibly go 50x175, but would suggest you go C24 50x200 to be way out on the right side and for aother reason, that will explain later.
Now using 200 deep rafters your HAP will be approx 150 above plate. Your apex will be the same, but at plate level will be 150 higher thereby decreasing your true pitch from 15.74 to 13.41 degrees up the rafter. You could get this back if you wished, providing bedroom widow is 1200 deep by changing window for 1050 deep and two course of new brickwork in opening. New brickwork will not be seen as it will be covered by lead flashing. There is one other way of increasing your roof up to 25 plus degrees but a lot of work is involved and is to complicated for us to explain on here.
Tiles. If you leave pitch at 13 degrees, you are limited on tile choice. You only have Redland Regent through colour or Forticrete Centurion, Both of these tiles have a roll, whereas if you had been at 15 degree this would have given you a lot more choice.
Your problem now is your binders. We would have solved all these problems by making up two half TDA trusses with stub toe for building in and supported binders and purlins of these. Much to complicated for us to explain on here how to make these up, but tomorrow will come back with a suggestion for you to put to BC. Have things to do now. Be back to-morrow
This may be difficult for you to understand, but if you read it two or three times it will come to you.
oldun
Binders. Length of building 25ft = 7260 less two external skins and two cavities = 400 = 6860 overall span. Now you are bu**ered unless you have a centre internal load bearing wall from back of existing house to new extension back wall to sit binders on. Let me know, is it one room, or split in two?
Pitch. Depth of building 3660 less face wall and cavity 200 = 3460, therefore back of wall plate to existing house = half span of 3460.
Window is 16 course to under sill from top of plate = 1200 less 225 to allow for 150 lead flashing and 75 for batten and tile girth = rise of 975. Therefore 3460 half span and 975 rise gives hypotenuse of 3594 and pitch of 15.74 degrees.
However this is not the pitch of the finished roof as you now have to take into consideration the height of the rafter above plate. This is called HAP. Before going any further, lets look at rafter size. As it is uneconomical to use rafters deeper than 150 the tables only go up to 150 depth and then you start using purlins. You can go 3520 on a 50x150 rafter without using a purlin, but as you will be outside this measure, you could possibly go 50x175, but would suggest you go C24 50x200 to be way out on the right side and for aother reason, that will explain later.
Now using 200 deep rafters your HAP will be approx 150 above plate. Your apex will be the same, but at plate level will be 150 higher thereby decreasing your true pitch from 15.74 to 13.41 degrees up the rafter. You could get this back if you wished, providing bedroom widow is 1200 deep by changing window for 1050 deep and two course of new brickwork in opening. New brickwork will not be seen as it will be covered by lead flashing. There is one other way of increasing your roof up to 25 plus degrees but a lot of work is involved and is to complicated for us to explain on here.
Tiles. If you leave pitch at 13 degrees, you are limited on tile choice. You only have Redland Regent through colour or Forticrete Centurion, Both of these tiles have a roll, whereas if you had been at 15 degree this would have given you a lot more choice.
Your problem now is your binders. We would have solved all these problems by making up two half TDA trusses with stub toe for building in and supported binders and purlins of these. Much to complicated for us to explain on here how to make these up, but tomorrow will come back with a suggestion for you to put to BC. Have things to do now. Be back to-morrow
This may be difficult for you to understand, but if you read it two or three times it will come to you.
oldun
. Now you are bu**ered unless you have a centre internal load bearing wall from back of existing house to new extension back wall to sit binders on. Let me know, is it one room, or split in two?
However this is not the pitch of the finished roof as you now have to take into consideration the height of the rafter above plate. This is called HAP.
Thanks so much for the info....its a bit complex first off but good. I have a couple of questions about terminology....What is a purlin?....i've heard it before but not sure what it refers to.
Next.....when you say "rafter" can you be more specific in simpleton terms...(sorry).
Anyway....you asked if its one room....to be honest thats the plan.
I was not sure which way to set the ceiling joists (as its 25ft width ways) but i was hoping to set them the same way as the roof timbers....is this not possible?.
Also when you refer to timber size...what is "C16" ....obviously i know the size after that but what does the "C" and number refer to?.
Thanks so much
However this is not the pitch of the finished roof as you now have to take into consideration the height of the rafter above plate. This is called HAP.
Thanks so much for the info....its a bit complex first off but good. I have a couple of questions about terminology....What is a purlin?....i've heard it before but not sure what it refers to.
Next.....when you say "rafter" can you be more specific in simpleton terms...(sorry).
Anyway....you asked if its one room....to be honest thats the plan.
I was not sure which way to set the ceiling joists (as its 25ft width ways) but i was hoping to set them the same way as the roof timbers....is this not possible?.
Also when you refer to timber size...what is "C16" ....obviously i know the size after that but what does the "C" and number refer to?.
Thanks so much
Not if you double or treble a joist to form a beam to support the binders
Or drop some 4x2 hangers down to the binder from the rafters
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Will answer your questions first, but before doing so, will say in a very kind way, if you do not know what a purlin and rafter are, then I do not fancy your chances of pitching this roof on your own.
Rafter is the timber member that forms the slope on roof and supports felt, battens and tiles. It will pitch from the lower wall plate on the back skin of the back wall on new extension to the top wall plate fixed to your existing house.
Purlin is a large timber member that runs at right angles to your rafters and sits on the gable walls and supports your rafters either mid span or 1/3 and 2/3 span. The purlin enables you to reduce depth of rafters to make roof more economical to construct.
C16 and C24 are the new European grades for grading carcassing timber. All timber is graded usually at its point of origin to determine the strength. It is either done visual, mechanically or by species, and should then be stamped on timber. C24 is the strongest, but often difficult to obtain.
Was now going to tell you how to get round the binder problem, but have sat here thinking and have come to the conclusion that this roof is going to cost you a fortune, even if you can do it.
Have phoned Minerva Truss Co to-day 01978 758869, and they said it will be no problem to make you up Mono half trusses with a stub toe to build in at 600 centres. Believe me this will save you a lot money, and you can easily throw them up yourself. Strongly suggest you go this route and if you want any further help at all on how to fix trusses then come back. Google roof trusses then Minerva.
oldun
Rafter is the timber member that forms the slope on roof and supports felt, battens and tiles. It will pitch from the lower wall plate on the back skin of the back wall on new extension to the top wall plate fixed to your existing house.
Purlin is a large timber member that runs at right angles to your rafters and sits on the gable walls and supports your rafters either mid span or 1/3 and 2/3 span. The purlin enables you to reduce depth of rafters to make roof more economical to construct.
C16 and C24 are the new European grades for grading carcassing timber. All timber is graded usually at its point of origin to determine the strength. It is either done visual, mechanically or by species, and should then be stamped on timber. C24 is the strongest, but often difficult to obtain.
Was now going to tell you how to get round the binder problem, but have sat here thinking and have come to the conclusion that this roof is going to cost you a fortune, even if you can do it.
Have phoned Minerva Truss Co to-day 01978 758869, and they said it will be no problem to make you up Mono half trusses with a stub toe to build in at 600 centres. Believe me this will save you a lot money, and you can easily throw them up yourself. Strongly suggest you go this route and if you want any further help at all on how to fix trusses then come back. Google roof trusses then Minerva.
oldun
Oldun....your a gem. Thanks so much for your time and advice....really appreciated.
When you describe the purlin by what it does i understand....its just the jargon i'm not familiar with. Same with rafter.
I will check it out on google as you suggested and go from there.
Thanks again, a thousand times....
I've got the BC inspector coming in a couple of weeks after i finish bricking up the other side wall and go through with him what he wants and use a printed copy of your comments if he gets fussy.
Cheers mate
When you describe the purlin by what it does i understand....its just the jargon i'm not familiar with. Same with rafter.
I will check it out on google as you suggested and go from there.
Thanks again, a thousand times....
I've got the BC inspector coming in a couple of weeks after i finish bricking up the other side wall and go through with him what he wants and use a printed copy of your comments if he gets fussy.
Cheers mate
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