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rt1200
Hi BiggsSolar
I have read many of your posts and you come across as a professional person who wants to do the right thing, both for your customers, and your own peace of mind - so respect. With regard to your post this is what I think, it’s my personal opinion for what it’s worth. I hope you find this long winded reply helpful. It’s specifically about retrofit arrays to traditionally built slate roofs but many of the points/philosophy will apply to all installations.
All components of a structure will move, to varying degrees. Indeed many structures such as Skyscrapers are designed to move. We have all seen the results of not allowing for movement in structures and/or individual materials. Factors playing a part might include forces such as age, degradation, previous alterations, quality of original materials, workmanship and design, moisture and thermal movement, additional loadings, E.g. wind, snow, maintenance, etc. Most trades, when working on an existing structure, tend to assume that everything existing, built by other trades before is of a reasonable quality and standard, unless they see something obvious to the contrary.
So all of the components of your PV mounting system and the roof to which it’s mounted will 1. be constantly moving, 2. be placed under varying stresses, and 3. you will be making assumptions about the original build quality and current condition of the structures supporting it all. On one hand you want to firmly attach the system so as to resist forces such as wind and ensure a durable, weather-proof finish and on the other, you have to allow for some movement and the relative fragility of materials such as slate? I, like you, can see all sorts of potential issues occurring. If you want peace of mind you must have complete faith in the solution you choose and it needs to be thought about and planned. Frankly, it worries me when people says things like "we'll see how it goes" or "I’m not sure"!! So what to do?
1. A "good dependable" roofer should be employed to fit and weather proof the fixings.
2. Hanger Bolts are more appropriate for trapezoidal roofs - not slate where they are a defect waiting to happen. Roof anchors should be used that are designed for use with slated roofs. As an example see the Schuco range of aluminium and stainless steel roof fixings.
3. Slates need to be removed to fix the anchor. See the following rensol site link which indicates the general principle but I would do some things differently. See below 3a &b.
Solar PV Panels Lincolnshire |SOL 50 installation guide
3a. I would rather not screw fix into rafters. I would, wherever possible, drill and bolt right through the rafter with a plate or large washer, if you wish, on the other side and use a nylon lock tight nut. (Please remember, with any fixing, you need to be aware of the important relationship between the diameter of the fixing and the width of the rafter. Some rafters can be incredibly thin. Also the diameter of the fixing and the spacing between fixings. There is a simple formula table for both which any decent Building Control surveyor or structural engineer should have access to).
3b. If the rafter is thin and the anchor significantly wider I would use tannalised timber either side of the rafter to provide a proper seating for the anchor plate. I would also carefully check the slates battens before using them as "packing" between anchor and rafter. With different anchors supplementary packing may be required. However, the point of getting a good roofer is that he should be doing this for you. All this sounds like a lot but it doesn’t take that much longer than a bodge job and the extra materials are relatively inexpensive.
4. Flashband is not appropriate for this type of work. The appropriately coded lead, (or non-lead alternative), cover flashing needs to be sized for the anchor, the slate size and the lap. It’s better to have slightly more overlap than not quite enough. Similar in principle to any other protrusion such as a soil vent pipe. Generally, the lower the roof pitch and the smaller the slate lap the more careful you have to be. Again - get a good roofer for peace of mind!
4. There is slate and there is slate. The difference between Welsh Slate and Spanish slate is like comparing the driving abilities of the Stig and my wife! Spanish slates can sometimes break just if you look at them nastily! Another reason not to use hanger bolts or place anchor plates over slates, none of which, Welsh or Spanish, have tensile strength.
One last thing which is related and VERY IMPORTANT...........
In a nutshell if you add something, like a PV array, to an existing roof/structure and the loading on the roof is increased by 15% or more, then this is a material alteration under Part A of the Regulations and you require building Regulations approval. I think that this might apply to a significant number of PV systems. There is a Competent person’s scheme (CPS), - a bit like FENSA for window installers, if they are registered - you don’t need LA approval. However, is the MSC a CPS for the purposes of Part A of the Building Regulations? My personal opinion is no because this would mean your company is competent to carry out structural assessments of existing roof structures. (FYI At the end I have included a link to a best practice note on one of the many local government websites offering further advice on this. Please read it carefully and speak with your local building control if you have queries because they may all interpret it slightly differently. Indeed, many don’t really know much about it themselves, are confused and playing catch up - but they will in time - it is a legal requirement!). In any case, I would certainly want to know if a roof could take the loading.
The bottom line is not so much legal compliance, it’s about your reputation, your longevity as a business, about being sued and about peace of mind for you and your customers, whether its regarding a leaking roof or failure of the roof altogether!
I hope you find this useful. Unfortunately I don’t check this really good forum as regularly as I should so please don’t think me rude if I don’t respond further for ages. I’ve just written this because I’ve been nudged by Dan!!!
Best wishes and regards,
http://www.bolton.gov.uk/sites/documentcentre/Documents/LABC Solar panel.pdf
I have read many of your posts and you come across as a professional person who wants to do the right thing, both for your customers, and your own peace of mind - so respect. With regard to your post this is what I think, it’s my personal opinion for what it’s worth. I hope you find this long winded reply helpful. It’s specifically about retrofit arrays to traditionally built slate roofs but many of the points/philosophy will apply to all installations.
All components of a structure will move, to varying degrees. Indeed many structures such as Skyscrapers are designed to move. We have all seen the results of not allowing for movement in structures and/or individual materials. Factors playing a part might include forces such as age, degradation, previous alterations, quality of original materials, workmanship and design, moisture and thermal movement, additional loadings, E.g. wind, snow, maintenance, etc. Most trades, when working on an existing structure, tend to assume that everything existing, built by other trades before is of a reasonable quality and standard, unless they see something obvious to the contrary.
So all of the components of your PV mounting system and the roof to which it’s mounted will 1. be constantly moving, 2. be placed under varying stresses, and 3. you will be making assumptions about the original build quality and current condition of the structures supporting it all. On one hand you want to firmly attach the system so as to resist forces such as wind and ensure a durable, weather-proof finish and on the other, you have to allow for some movement and the relative fragility of materials such as slate? I, like you, can see all sorts of potential issues occurring. If you want peace of mind you must have complete faith in the solution you choose and it needs to be thought about and planned. Frankly, it worries me when people says things like "we'll see how it goes" or "I’m not sure"!! So what to do?
1. A "good dependable" roofer should be employed to fit and weather proof the fixings.
2. Hanger Bolts are more appropriate for trapezoidal roofs - not slate where they are a defect waiting to happen. Roof anchors should be used that are designed for use with slated roofs. As an example see the Schuco range of aluminium and stainless steel roof fixings.
3. Slates need to be removed to fix the anchor. See the following rensol site link which indicates the general principle but I would do some things differently. See below 3a &b.
Solar PV Panels Lincolnshire |SOL 50 installation guide
3a. I would rather not screw fix into rafters. I would, wherever possible, drill and bolt right through the rafter with a plate or large washer, if you wish, on the other side and use a nylon lock tight nut. (Please remember, with any fixing, you need to be aware of the important relationship between the diameter of the fixing and the width of the rafter. Some rafters can be incredibly thin. Also the diameter of the fixing and the spacing between fixings. There is a simple formula table for both which any decent Building Control surveyor or structural engineer should have access to).
3b. If the rafter is thin and the anchor significantly wider I would use tannalised timber either side of the rafter to provide a proper seating for the anchor plate. I would also carefully check the slates battens before using them as "packing" between anchor and rafter. With different anchors supplementary packing may be required. However, the point of getting a good roofer is that he should be doing this for you. All this sounds like a lot but it doesn’t take that much longer than a bodge job and the extra materials are relatively inexpensive.
4. Flashband is not appropriate for this type of work. The appropriately coded lead, (or non-lead alternative), cover flashing needs to be sized for the anchor, the slate size and the lap. It’s better to have slightly more overlap than not quite enough. Similar in principle to any other protrusion such as a soil vent pipe. Generally, the lower the roof pitch and the smaller the slate lap the more careful you have to be. Again - get a good roofer for peace of mind!
4. There is slate and there is slate. The difference between Welsh Slate and Spanish slate is like comparing the driving abilities of the Stig and my wife! Spanish slates can sometimes break just if you look at them nastily! Another reason not to use hanger bolts or place anchor plates over slates, none of which, Welsh or Spanish, have tensile strength.
One last thing which is related and VERY IMPORTANT...........
In a nutshell if you add something, like a PV array, to an existing roof/structure and the loading on the roof is increased by 15% or more, then this is a material alteration under Part A of the Regulations and you require building Regulations approval. I think that this might apply to a significant number of PV systems. There is a Competent person’s scheme (CPS), - a bit like FENSA for window installers, if they are registered - you don’t need LA approval. However, is the MSC a CPS for the purposes of Part A of the Building Regulations? My personal opinion is no because this would mean your company is competent to carry out structural assessments of existing roof structures. (FYI At the end I have included a link to a best practice note on one of the many local government websites offering further advice on this. Please read it carefully and speak with your local building control if you have queries because they may all interpret it slightly differently. Indeed, many don’t really know much about it themselves, are confused and playing catch up - but they will in time - it is a legal requirement!). In any case, I would certainly want to know if a roof could take the loading.
The bottom line is not so much legal compliance, it’s about your reputation, your longevity as a business, about being sued and about peace of mind for you and your customers, whether its regarding a leaking roof or failure of the roof altogether!
I hope you find this useful. Unfortunately I don’t check this really good forum as regularly as I should so please don’t think me rude if I don’t respond further for ages. I’ve just written this because I’ve been nudged by Dan!!!
Best wishes and regards,
http://www.bolton.gov.uk/sites/documentcentre/Documents/LABC Solar panel.pdf
