Hi,
someone recommended i ask you this question as you may be able to help a little.
Scenario/Info:
Currently in the planning stages, already submitted and approved by planning office, but not yet submitted for building regulation, however the building inspector has visited and given a little advice on the plans before i submit them.
Following his visit, i will be making a couple of minor changes regarding the roofing material and ventilation, and resubmitting the plans for planning approval (have already submitted a change request and because of a minor increase in height and roofing material to be used, the planners want the whole thing re-submitting, although no major problems are expected, it just cant be accepted as minor alterations to the plans)
ok, so here's the basics, as originally planned,
16 degree roof, spanning from the ridge of the original house roof, extending a total of 10.5m, to be supported at 3 purlin points, plus the original ridge line and the exterior of the new extension. Roofing tiles planned were Redland Regent tudor brown.
Roof has 2 upper velux windows into loft room, and 3 lower ones into sunroom/conservatory.
All was ok, except the low pitch was close to the limits of the tiles.
Following successful planning approval, the architects structural engineer did the calculations, and presented us with the paperwork specifying materials support points etc..... this is where we hit problems.
For the purlin supports, he specified 3, 2 are directly above what are/ were exterior cavity calls with foundations (property was extended once) these were no problems, the third, he has specified is the first support down from the ridge line, and it runs through the middle of the upper 2 velux window positions, and it's vertical support runs through the middle of a 70 gallon water tank position, which can not be moved to another location.
so... back we went to the architect and pointed out this was not acceptable, he then reported back that the support beam could not be moved, due to the canter leaver of the section between it and the ridge line, and also the weight.
at this point, i had the building inspector visit, and i pitched the idea of using 'Ondutile' under sheeting to add additional weather protection to the roof due to the angle, and also to help me with the possibility of moving the support point i suggested using a 'Decra Classic light weight tile system' both of these ideas he was more than happy with, being already familiar with the Ondutile system, and he preferred the Decra system over the use of concrete tiles bearing in mind the pitch involved and the weight.
So, back i go to the architect, reply was that the structural engineer could move the support out 1/2 a metre to support from the points the original steeper pitched roof's purlin was supported, basically directly above them (we are not planning on removing the original purlin or rafters, simply building 'overhead' of them, so the original points and rafters are carrying virtually no weight.... this clears the water tank, but not the windows, to do this i need to move a further 1/2 metre away from the ridge line, increasing the span.
I am basically getting a "no" from the architect on this, and virtually no information back from the structural engineer.
So i started scrutinising the calculations and materials specified, for the rafters he has specified 5x2 C16 grade ....... so finally, here is my question to you now i have given you a little info to work with ...
Question
if i change the specified rafters to 6x2 C24 grade will this give me an increase in spanable distance between support points over the originally specified ones, given the same roofing materials and pitch... ??
as i see it, with the substantial decrease in weight (on both pitches of the roof) and the increase in rafter sizes and grade on the lower pitched side, i should have gained some flexibility n the positioning of the support points
sorry its been a long post/question
I will probably be using a different structural engineer to recalculate everything prior to submitting as i can't say i'm overly happy with this chap, but as you know, these chaps arent cheap and if i'm barking up the wrong tree so to speak, i could potentially flush a bunch of money down the drain for no reason.... i have had a family friend look at the structural engineers paperwork, as he used to be an architect and he said that it appears the guy has done little but taken what could be considered 'standard practises and materials' and produced the calculations and support points based on those, rather than seeing what was required and what space was available and selected materials that fitted those requirements of extended spans.
someone recommended i ask you this question as you may be able to help a little.
Scenario/Info:
Currently in the planning stages, already submitted and approved by planning office, but not yet submitted for building regulation, however the building inspector has visited and given a little advice on the plans before i submit them.
Following his visit, i will be making a couple of minor changes regarding the roofing material and ventilation, and resubmitting the plans for planning approval (have already submitted a change request and because of a minor increase in height and roofing material to be used, the planners want the whole thing re-submitting, although no major problems are expected, it just cant be accepted as minor alterations to the plans)
ok, so here's the basics, as originally planned,
16 degree roof, spanning from the ridge of the original house roof, extending a total of 10.5m, to be supported at 3 purlin points, plus the original ridge line and the exterior of the new extension. Roofing tiles planned were Redland Regent tudor brown.
Roof has 2 upper velux windows into loft room, and 3 lower ones into sunroom/conservatory.
All was ok, except the low pitch was close to the limits of the tiles.
Following successful planning approval, the architects structural engineer did the calculations, and presented us with the paperwork specifying materials support points etc..... this is where we hit problems.
For the purlin supports, he specified 3, 2 are directly above what are/ were exterior cavity calls with foundations (property was extended once) these were no problems, the third, he has specified is the first support down from the ridge line, and it runs through the middle of the upper 2 velux window positions, and it's vertical support runs through the middle of a 70 gallon water tank position, which can not be moved to another location.
so... back we went to the architect and pointed out this was not acceptable, he then reported back that the support beam could not be moved, due to the canter leaver of the section between it and the ridge line, and also the weight.
at this point, i had the building inspector visit, and i pitched the idea of using 'Ondutile' under sheeting to add additional weather protection to the roof due to the angle, and also to help me with the possibility of moving the support point i suggested using a 'Decra Classic light weight tile system' both of these ideas he was more than happy with, being already familiar with the Ondutile system, and he preferred the Decra system over the use of concrete tiles bearing in mind the pitch involved and the weight.
So, back i go to the architect, reply was that the structural engineer could move the support out 1/2 a metre to support from the points the original steeper pitched roof's purlin was supported, basically directly above them (we are not planning on removing the original purlin or rafters, simply building 'overhead' of them, so the original points and rafters are carrying virtually no weight.... this clears the water tank, but not the windows, to do this i need to move a further 1/2 metre away from the ridge line, increasing the span.
I am basically getting a "no" from the architect on this, and virtually no information back from the structural engineer.
So i started scrutinising the calculations and materials specified, for the rafters he has specified 5x2 C16 grade ....... so finally, here is my question to you now i have given you a little info to work with ...
Question
if i change the specified rafters to 6x2 C24 grade will this give me an increase in spanable distance between support points over the originally specified ones, given the same roofing materials and pitch... ??
as i see it, with the substantial decrease in weight (on both pitches of the roof) and the increase in rafter sizes and grade on the lower pitched side, i should have gained some flexibility n the positioning of the support points
sorry its been a long post/question
I will probably be using a different structural engineer to recalculate everything prior to submitting as i can't say i'm overly happy with this chap, but as you know, these chaps arent cheap and if i'm barking up the wrong tree so to speak, i could potentially flush a bunch of money down the drain for no reason.... i have had a family friend look at the structural engineers paperwork, as he used to be an architect and he said that it appears the guy has done little but taken what could be considered 'standard practises and materials' and produced the calculations and support points based on those, rather than seeing what was required and what space was available and selected materials that fitted those requirements of extended spans.
