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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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Size of wood beams? Corrugated roof?
Hi,
Thanks for the previous help with cement bag sizes, that bit is in place now. Q1. The beams are to support a light weight corrugated flat roof of internal size 8' x 15'. Beam spacing will be a little under every 2 foot with the 5 beams running the length of the 15 foot with two sets of bracing noggins at 5' in from each ends. Unsupported span is 15 feet. Ends will be firmly fixed down to structure and protruding through walls. Will 5" x 2.5" (actual sawn size) be adequate? Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? -- Regards, Harry (M1BYT) (L) http://www.ukradioamateur.co.uk |
#2
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Size of wood beams? Corrugated roof?
Harry Bloomfield wrote:
Hi, Thanks for the previous help with cement bag sizes, that bit is in place now. Q1. The beams are to support a light weight corrugated flat roof of internal size 8' x 15'. Beam spacing will be a little under every 2 foot with the 5 beams running the length of the 15 foot with two sets of bracing noggins at 5' in from each ends. Unsupported span is 15 feet. Ends will be firmly fixed down to structure and protruding through walls. Will 5" x 2.5" (actual sawn size) be adequate? 15ft unsupported span is far too long, the beams will sag, is there no possibility of going the opposite way and using 8ft beams?....failing that, I fear it will require a purlin in the centre, possibly steel. Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? OSB boards, overlaid with torch-on roof felt |
#3
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Size of wood beams? Corrugated roof?
Harry Bloomfield wrote:
Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? Corrugated iron over Sterling board. You could use Onduline or similar, but... well, I really wouldn't. |
#4
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Size of wood beams? Corrugated roof?
The message
from Harry Bloomfield contains these words: Q1. The beams are to support a light weight corrugated flat roof of internal size 8' x 15'. Beam spacing will be a little under every 2 foot with the 5 beams running the length of the 15 foot with two sets of bracing noggins at 5' in from each ends. Unsupported span is 15 feet. Ends will be firmly fixed down to structure and protruding through walls. Will 5" x 2.5" (actual sawn size) be adequate? Probably. If it was a floor you would want 9" x 2" joists to span 15' but you don't want to load it with anything more than wind and your own weight as you fix it down. Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? I think you will find that modern corrugated sheet does not contain asbestos. Plastic covered steel is an alternative. I can't remember what it is called but it has a section something like (IIRC) _____ ______ _/ \_____/ \_ and is a doddle to fit. You don't say which way the roof slopes but the beam layout suggests it is down the short dimension. However should you want it to slope down the long dimension the steel sheets can be ordered in in quite long lengths, I think in excess of 15'. -- Roger Chapman |
#5
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Size of wood beams? Corrugated roof?
Harry Bloomfield wrote:
Hi, Thanks for the previous help with cement bag sizes, that bit is in place now. Q1. The beams are to support a light weight corrugated flat roof of internal size 8' x 15'. Beam spacing will be a little under every 2 foot with the 5 beams running the length of the 15 foot with two sets of bracing noggins at 5' in from each ends. Unsupported span is 15 feet. Ends will be firmly fixed down to structure and protruding through walls. Will 5" x 2.5" (actual sawn size) be adequate? Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? sagulator will give you a figure for how much sag you can expect under any given load. http://www.woodbin.com/calcs/sagulator.htm Then you can decide of the amount of sag will look ok. Over 15' it would have to sag a foot or so before breaking. You dont say whether this needs to be BR compliant, if so there are different rules to follow. Dont forget to calculate for snow loading, roofs must survive that ok. NT |
#6
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Size of wood beams? Corrugated roof?
"Harry Bloomfield" wrote in message ... Q1. The beams are to support a light weight corrugated flat roof of internal size 8' x 15'. Beam spacing will be a little under every 2 foot with the 5 beams running the length of the 15 foot with two sets of bracing noggins at 5' in from each ends. Unsupported span is 15 feet. Ends will be firmly fixed down to structure and protruding through walls. Will 5" x 2.5" (actual sawn size) be adequate? I've just built a garage with 16ft span, using 8x2 at 4ft centres. My gut feeling is that 5" is a bit light, and the joists will sag visibly under their own weight. Bearing in mind that deflection is inversely proportional to the cube of the depth, even a modest increase in depth makes a big difference (e.g. 5" deflects 4 times as much as 8" for the same total load). If you decide to do proper calcs, the deflection and maximum stress are the easy bits - deciding on the wind load is the tricky bit. Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? Box section steel sheet is about 6 quid a square metre, and is available in long lengths, so you could get away with no end laps at all. Minimum suggested pitch is 5 degrees iirc, or about 1 in 12. Fibre cement sheets are only available in shorter lengths ( 3m ?) and really need a steeper pitch, particularly if they're laid such that there are end laps, despite the practice of makers of cheap concrete garages. The problem with steel sheets is that the insulation value is minimal, and you'll get condensation dripping off the underside in some conditions. The design of insulated roofs with vapour barriers etc is quite a complicated business: my compromise was to deck the roof with secondhand 18mm ply then cover it in polythene, then clad in steel. The SLE Cladding site is helpful. -- Kevin Poole **Use current month and year to reply (e.g. )*** |
#7
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Size of wood beams? Corrugated roof?
Autolycus wrote:
"Harry Bloomfield" wrote in message ... Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? Box section steel sheet is about 6 quid a square metre, and is available in long lengths, so you could get away with no end laps at all. Minimum suggested pitch is 5 degrees iirc, or about 1 in 12. Fibre cement I'm not sure what you refer to here, can you give us a link or soemthing? thanks, NT |
#8
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Size of wood beams? Corrugated roof?
wrote in message ups.com... Autolycus wrote: "Harry Bloomfield" wrote in message ... Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? Box section steel sheet is about 6 quid a square metre, and is available in long lengths, so you could get away with no end laps at all. Minimum suggested pitch is 5 degrees iirc, or about 1 in 12. Fibre cement I'm not sure what you refer to here, can you give us a link or soemthing? http://coruspanelsandprofiles.co.uk/ then Products and services Roofs Site assembled Standard roof profiles View Profiles R32-1000 takes you (I hope) to some basic data on one of the most common profiles. I was wrong: it's 4 degrees (1 in 15). Note that it's also often found in 0.5mm thickness, which imho is a bit thin unless you support in continuously, as I did. -- Kevin Poole **Use current month and year to reply (e.g. )*** |
#9
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Size of wood beams? Corrugated roof?
Autolycus wrote:
wrote in message ups.com... Autolycus wrote: "Harry Bloomfield" wrote in message ... Q2. What is a good cost effective alternative to asbestos cement corrugated roof panels? Box section steel sheet is about 6 quid a square metre, and is available in long lengths, so you could get away with no end laps at all. Minimum suggested pitch is 5 degrees iirc, or about 1 in 12. Fibre cement I'm not sure what you refer to here, can you give us a link or soemthing? http://coruspanelsandprofiles.co.uk/ then Products and services Roofs Site assembled Standard roof profiles View Profiles R32-1000 takes you (I hope) to some basic data on one of the most common profiles. I was wrong: it's 4 degrees (1 in 15). Note that it's also often found in 0.5mm thickness, which imho is a bit thin unless you support in continuously, as I did. thanks Kevin. What a horrible website. NT |
#10
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Size of wood beams? Corrugated roof?
Harry Bloomfield wrote: Hi, Q1. The beams are to support a light weight corrugated flat roof of internal size 8' x 15'. Beam spacing will be a little under every 2 foot with the 5 beams running the length of the 15 foot with two sets of bracing noggins at 5' in from each ends. Unsupported span is 15 feet. Depending on the time and trouble you want to take, you might want to use a structure like designed by the mathematician John Wallis "Wallis tackled a practical problem - how to provide a flat structure such as a roof to span a large square open space, using only wooden beams much shorter than the required span and only supported around the edges. He devised a repeating pattern of short but interlocking beams, which could be extended to span any sized space." See URL:http://www.soue.org.uk/souenews/issue4/wallis.html As it turned out, this design wasn't used for the internal roof of the Sheldonian Theatre, Oxford - Wren used a different technique - a composite roof truss. Cheers, Sid. |
#11
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Size of wood beams? Corrugated roof?
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