How do the Private Messaging you speak of Tony1851
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- Thread starter chirpychippy
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How do the Private Messaging you speak of Tony1851
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Cheers for your post Tony, agree with most of it, but disagree with your approach.
The Lads drawings are sh*te, reckon they were for P.P. only and the work is being carried out on a B.N., hence the lack of information.
In an instance like this if he works to Trada tables and there is any problem from B.C. with timber sizing, then all he needs do is refer B.C. to span tables, and without being cheeky to you. not having to say that Tony from Manchester told him that 47x200 would comply.
However if you will size all his timbers along with the required calculations, then I feel sure he will be for ever in your debt.
Look forward to your post, in the mean time, we will post to the Lad tomorrow, what we consider should be all his timber sizes and the easiest way to pitch a salt box.
Regards oldun
@ Oldun; agree 100% - it's the perennial problem with an internet forum - what to believe and what not to.
The drawings are clearly planning-application drawings where no thought has been given as to how to actually build it - hence the usual 'do-it-on-a-Building-Notice' cop-out by the plan-drawer.
Personally I stand by the 2x8s but as you say, the inspector will go by the tables and not some bod on a forum. Possibly the way forward would be to include a purlin, but to try and get the inspector to agree to a size without providing calcs, even if it was overkill?
The drawings are clearly planning-application drawings where no thought has been given as to how to actually build it - hence the usual 'do-it-on-a-Building-Notice' cop-out by the plan-drawer.
Personally I stand by the 2x8s but as you say, the inspector will go by the tables and not some bod on a forum. Possibly the way forward would be to include a purlin, but to try and get the inspector to agree to a size without providing calcs, even if it was overkill?
I think you think Iam taking the p**s by posting on this forum and basically asking others to work out my roofs for me, to a degree iI am asking a bit more than I should, I know this.
However, if I dont take on these sorts of jobs then I don't learn.
I have bought the book of Trada span tables so at least i can learn this form of calculating rafters purlins binders etc, I would like to learn to do it with math as well.
The drawings i posted are sh*te. I have since spoken to builder and asked for any other drawings plans schedules etc which are a bit more informative, Iam now in receipt of the Final plans which clearly show a Flich Beam at the iintersection of the ceiling joists and the front rafters, although there are no calcs on this at present it is in hands of structural engineer.
I have also spoken in great detail with the architect on some structural elements which has appeased me.
I am now awaiting the book and if all else fails I will use 8x2 and speak to a BCO, thank you for your help, I do appreciate it and realistically I will forever be in debt of those that help me.
Thank you Chirpy
However, if I dont take on these sorts of jobs then I don't learn.
I have bought the book of Trada span tables so at least i can learn this form of calculating rafters purlins binders etc, I would like to learn to do it with math as well.
The drawings i posted are sh*te. I have since spoken to builder and asked for any other drawings plans schedules etc which are a bit more informative, Iam now in receipt of the Final plans which clearly show a Flich Beam at the iintersection of the ceiling joists and the front rafters, although there are no calcs on this at present it is in hands of structural engineer.
I have also spoken in great detail with the architect on some structural elements which has appeased me.
I am now awaiting the book and if all else fails I will use 8x2 and speak to a BCO, thank you for your help, I do appreciate it and realistically I will forever be in debt of those that help me.
Thank you Chirpy
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I doubt that anyone here would think you are taking the pi$$ - questions are what a forum is supposed to be for.
If you are a builder/joiner, the best way forward for sizing timber joists and rafter etc is to either get the plan-drawer to tell you the sizes (thus taking the responsibility off you); or, look the sizes up in the tables.
As mentioned previously, calculating the sizes required almost always gives you smaller section-sizes (or alternatively slightly longer spans for a given section). But unfortunately there is no one 'formula' or easy-to-understand way of doing it and you won't find it in one book either.
The maths is straightforward - especially so with a calculator! - it's the principles and knowing which factors to apply which takes time and practice to learn and you just can't get that off a forum.
But good luck with the roof anyway.
If you are a builder/joiner, the best way forward for sizing timber joists and rafter etc is to either get the plan-drawer to tell you the sizes (thus taking the responsibility off you); or, look the sizes up in the tables.
As mentioned previously, calculating the sizes required almost always gives you smaller section-sizes (or alternatively slightly longer spans for a given section). But unfortunately there is no one 'formula' or easy-to-understand way of doing it and you won't find it in one book either.
The maths is straightforward - especially so with a calculator! - it's the principles and knowing which factors to apply which takes time and practice to learn and you just can't get that off a forum.
But good luck with the roof anyway.
Chirpy,
Firstly nobody thinks you are taking the P*ss with the questions you are asking. You will find people on this forum are only to pleased to help you. One of our big regrets, is that over our life time we have only brought 4 apprentices through the trade
Some how or other you have altered your home page and it is now private and none of your drawings will come up. .Last night was the first time that we really looked at your drawings and would advise that there are details that just will not work on the present design.
If you alter your home oage so that your drawings will come up then we will run through them with you.
One other important thing, as Tony has said, always pass the buck and get your instructions or variation orders in writing.
Regards oldun.
Firstly nobody thinks you are taking the P*ss with the questions you are asking. You will find people on this forum are only to pleased to help you. One of our big regrets, is that over our life time we have only brought 4 apprentices through the trade
Some how or other you have altered your home page and it is now private and none of your drawings will come up. .Last night was the first time that we really looked at your drawings and would advise that there are details that just will not work on the present design.
If you alter your home oage so that your drawings will come up then we will run through them with you.
One other important thing, as Tony has said, always pass the buck and get your instructions or variation orders in writing.
Regards oldun.
Could you try again please Oldun as my settings are such that all registered users can view my profile pictures etc, please let me know, regards Chippy.
Tried again. Comes up Private Profile, no albums to view.
On your home page go into help and change your settings.
Regards oldun
Hello Oldun nothing in my settings to say I have a Private Profile so I am trying this out.
Tony, did you check deflection in the short and medium term conditions?
'Cos it looks to me like 200x50s are struggling a bit...
Chirpy,
Finally got your drawings up.. If it was us we would walk away, until somebody provided some decent working drawings, as the present drawings are just not workable or practical.
Take section first, Shows joists running front to back, but no partition or steel in centre to support this span. Gives one measurement only, 2400 storey height, Will come back to this later.
Side Elevation.
Left hand side of pair of doors shows 300 cavity wall with 90 degree return towards flank wall of house then 90 degree internal return to rear wall of extension. Is this all cavity wall and if so what is it sitting on? Or if it is studwork, what is it sitting on? The rectangle section of the first floor joist that will be left open, How is this to be waterproofed? Back wall of extrusion shows a 300 cav wall with plate at 2400?.on both existing house and new extension. It is just not possible to do this as you will not be able to fit gutter to extension or be able to get cover flashing for tiles to roof extension under existing house verge. The plate for the extension needs to be 300 lower than house to get gutter and cover flashing in and this will give you a storey height of 2100, unless you bolt ceiling joists to rear rafters to form a raised tie. Just had another butchers at the comic and it would appear dormer ceiling is at 2100 same height as door frame and back plate is also at 2100,. even though the section states 2400 Nothing makes sense. Remember Lad, never scale, only work to measurements With regard to main saltbox, as ridge is off set to return wall left hand side of doors, you will have a great big hole up there with nothing to fix your finish to,
Forgot to say it would appear that front curtain wall under dormer appears to be in studwork..
See no problem with dormer, but due to lack of information you may just need a treble up the sides.
The easy way to do a salt box Chirpy is to either put in hefty purlin, flitch beam or steel, whether you need it or not. Two reasons. 1. Hang or place joists on beam to relieve load on rafters, and to give you a working platform for top ridge and 2. split long rafters into two to make it more easy to pitch. We know it means an extra birds mouth and birds beak per rafter, but at the end of the day is much more quicker.
Without further info, that is about all the help we can give you. Not trying to teach you to suck eggs, But if you have bought Trada tables and want any help with them, then let us know. We work out our length of rafters with natural secants, but Ralph Goss Roofing Ready Reckoner is about the best you can buy, if you have not got it already.
If you want to know an easy way to work out pitch, rise, run and slope then let me know.
See yer oldun
Finally got your drawings up.. If it was us we would walk away, until somebody provided some decent working drawings, as the present drawings are just not workable or practical.
Take section first, Shows joists running front to back, but no partition or steel in centre to support this span. Gives one measurement only, 2400 storey height, Will come back to this later.
Side Elevation.
Left hand side of pair of doors shows 300 cavity wall with 90 degree return towards flank wall of house then 90 degree internal return to rear wall of extension. Is this all cavity wall and if so what is it sitting on? Or if it is studwork, what is it sitting on? The rectangle section of the first floor joist that will be left open, How is this to be waterproofed? Back wall of extrusion shows a 300 cav wall with plate at 2400?.on both existing house and new extension. It is just not possible to do this as you will not be able to fit gutter to extension or be able to get cover flashing for tiles to roof extension under existing house verge. The plate for the extension needs to be 300 lower than house to get gutter and cover flashing in and this will give you a storey height of 2100, unless you bolt ceiling joists to rear rafters to form a raised tie. Just had another butchers at the comic and it would appear dormer ceiling is at 2100 same height as door frame and back plate is also at 2100,. even though the section states 2400 Nothing makes sense. Remember Lad, never scale, only work to measurements With regard to main saltbox, as ridge is off set to return wall left hand side of doors, you will have a great big hole up there with nothing to fix your finish to,
Forgot to say it would appear that front curtain wall under dormer appears to be in studwork..
See no problem with dormer, but due to lack of information you may just need a treble up the sides.
The easy way to do a salt box Chirpy is to either put in hefty purlin, flitch beam or steel, whether you need it or not. Two reasons. 1. Hang or place joists on beam to relieve load on rafters, and to give you a working platform for top ridge and 2. split long rafters into two to make it more easy to pitch. We know it means an extra birds mouth and birds beak per rafter, but at the end of the day is much more quicker.
Without further info, that is about all the help we can give you. Not trying to teach you to suck eggs, But if you have bought Trada tables and want any help with them, then let us know. We work out our length of rafters with natural secants, but Ralph Goss Roofing Ready Reckoner is about the best you can buy, if you have not got it already.
If you want to know an easy way to work out pitch, rise, run and slope then let me know.
See yer oldun
Rummaged through the waste bin but couldn't find that dammed envelope!
Doing it again to EC5, and assuming the rafters were flat rather than inclined, I think the long-term deflection would be about 50mm. Recommended deflection for roofs without plasterboard = span/150 = 41mm therefore FAIL!.
But IIRC, on the original figures, I resolved the loads into forces normal to the beam, on the basis that, propped up against a wall at 40 deg, it wouldn't deflect as muchas if it were horizontal. Whether that's right or wrong I don't know, but it just seemed logical.
On that basis, I figure the deflection might just come under the limit, but I agree it's too close, and maybe 2x9s or 2x10s would be better. In that case, might be cheaper to use a purlin after all.
I have to hold my hands up and say you're right - you beat me on this one!
Thank you very much for your very in depth reply Oldun this has given me plenty of food for thought. I am going back to the contractor to ask that he in turn speaks to the Architect and obtains some working drawings, but in the mean time I am going to answer your questions as best as I can and share with you the way in which I have been advised to pitch this roof by another party.
Firstly the existing structure is brickwork exterior 75mm cavity block work interior to both the garage and utility extension to the rear. On top of this we have 8x2 floor joists at 400 cc hung off of the existing property on Galvanised brick hangers across the width of the garage and small extension. Around the perimeter of the garage and utility and directly above the brickwork we have an 8x2 x 90mm Ring beam. The gap under the ring beam is taken up with a plate to the top of the brick work and then 4x2 studs at 400cc to the underside of the ring beam.
The Frame work is being built out of 4x2 C24 at 400cc clad externally with 12mm ply, building paper, baton then counter baton then tile hung. All the insulation is going in between studs and over internally. " I was not happy when I learnt that this was being formed in 4x2 so I checked with Architect and he stated that it is ok but really should have been formed in 6x2"
O.K The 2.4 you see written on the cut through on the plan is written by me, because I scaled it off of the plan in lieu of having no dimensions.
THE IMPORTANT BIT. At the intersection of the ceiling joists to the front rafters there is going to be a flitch beam "the size of which is still in the hands of the SE" This isn't shown on the drawings I have uploaded but if you want to see it I can upload the drawing it is shown on, however, this drawing is just s useless as the rest.
I understand you point about the top of the rafters being to close to the underside of the gable end rafters of the existing roof with regards to flashing guttering etc. The storey height to my mind has been set at 2.4 as it marries with the existing storey height in the existing building, but I did scale it off the plan. The storey height for the dormer may well be 2.1 but when you look at the cut through section you can see the storey height of the main ceiling joists has to be higher?
This is a solution I have been presented with by someone that knows a lot more than I do.
Bearing in mind there is a flitch steel. Rafters to be 6x2 C24 at 400cc, triple up rafters to dormer sides.
Main Roof Front: Birds mouth rafters over wall plate and flitch beam. At midway point between flitch beam and ridge introduce 5x3 Purlin to both sides of main roof. From ridge on main roof drop down a King Post half lapped over ridge then half lapped over ceiling joist. Strut the purlins to the sides of the king post/s then introduce a sizeable binder bolted to the King Post/s and housed into the gable wall of main house collecting all the joists until it intersects with 4x2 Framework of the extension.
The smaller salt box roof can be formed in exactly the same way using 5x3 purlins, king posts, struts and binders.
I have spoken to the contractor to ask for clarification of the ceiling height and all the points you have raised, Please may I have your views on the above rafter sizing purlins king posts binders etc.
BTW This entire second storey extension was originally designed on the plans to go up in brick and block work, it was the contractor that changed it to timber framing at 4 x 2 which prompted my call directly to the architect. But architect is happy with 4 x2.
Thank you. Tony 1851 and Oldun
Firstly the existing structure is brickwork exterior 75mm cavity block work interior to both the garage and utility extension to the rear. On top of this we have 8x2 floor joists at 400 cc hung off of the existing property on Galvanised brick hangers across the width of the garage and small extension. Around the perimeter of the garage and utility and directly above the brickwork we have an 8x2 x 90mm Ring beam. The gap under the ring beam is taken up with a plate to the top of the brick work and then 4x2 studs at 400cc to the underside of the ring beam.
The Frame work is being built out of 4x2 C24 at 400cc clad externally with 12mm ply, building paper, baton then counter baton then tile hung. All the insulation is going in between studs and over internally. " I was not happy when I learnt that this was being formed in 4x2 so I checked with Architect and he stated that it is ok but really should have been formed in 6x2"
O.K The 2.4 you see written on the cut through on the plan is written by me, because I scaled it off of the plan in lieu of having no dimensions.
THE IMPORTANT BIT. At the intersection of the ceiling joists to the front rafters there is going to be a flitch beam "the size of which is still in the hands of the SE" This isn't shown on the drawings I have uploaded but if you want to see it I can upload the drawing it is shown on, however, this drawing is just s useless as the rest.
I understand you point about the top of the rafters being to close to the underside of the gable end rafters of the existing roof with regards to flashing guttering etc. The storey height to my mind has been set at 2.4 as it marries with the existing storey height in the existing building, but I did scale it off the plan. The storey height for the dormer may well be 2.1 but when you look at the cut through section you can see the storey height of the main ceiling joists has to be higher?
This is a solution I have been presented with by someone that knows a lot more than I do.
Bearing in mind there is a flitch steel. Rafters to be 6x2 C24 at 400cc, triple up rafters to dormer sides.
Main Roof Front: Birds mouth rafters over wall plate and flitch beam. At midway point between flitch beam and ridge introduce 5x3 Purlin to both sides of main roof. From ridge on main roof drop down a King Post half lapped over ridge then half lapped over ceiling joist. Strut the purlins to the sides of the king post/s then introduce a sizeable binder bolted to the King Post/s and housed into the gable wall of main house collecting all the joists until it intersects with 4x2 Framework of the extension.
The smaller salt box roof can be formed in exactly the same way using 5x3 purlins, king posts, struts and binders.
I have spoken to the contractor to ask for clarification of the ceiling height and all the points you have raised, Please may I have your views on the above rafter sizing purlins king posts binders etc.
BTW This entire second storey extension was originally designed on the plans to go up in brick and block work, it was the contractor that changed it to timber framing at 4 x 2 which prompted my call directly to the architect. But architect is happy with 4 x2.
Thank you. Tony 1851 and Oldun
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