Jml Posted June 11, 2020 Share Posted June 11, 2020 As part of our refurbishment we are converting part of our loft to a bathroom. The loft was part of a late 80’s early 90’s extension. The joists at present are 50 x 170 with a maximum span of 3930 at 400 centres. According to span tables I can find free on the net, the load up to 0.5 if c24 can span 3.88m. As the room will be a bathroom I will have to double the joists anyway. Questions How do I tell if the are C24 or not.? When using span tables is load up to 0.5 sufficient for first floor ? Would doubling of joists be sufficient for my new bathroom? Any help much appreciated. Jenny Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2020 Share Posted June 11, 2020 If this is being done under building regs then you will need to prove to BCO that this is acceptable. In terms of loading, static loading of 0.5 is used for clear floors with light loading. If you add stud walls then 0.75-1 is where you should be planning to stop movement. All tables for floor joists assume a dynamic 1.5 loading in addition which is where your bath/shower etc come in. Assuming you currently have 44 x170 joists then your maximum span would be at C16 3.963m under BS 5268-7.3, and that is for a ceiling joist. Convert this to a floor joist and then take the consideration in BS 6399-1 which is the new standard, then to get your spans you are borderline on using 88x170, or double up joists. These would need to be bolted together - not screwed - at 600mm centres to ensure the strength is reached. 1 Link to comment Share on other sites More sharing options...
Jml Posted June 11, 2020 Author Share Posted June 11, 2020 Many thanks for your response. BCO are involved, as will a SE,. I assume that there is some variation in actual widths of joists as have measured a few and nearer to 50 than 44? But being 44 and c16 makes sense. Bolting the existing ceiling joists with others c24 44x 170 But leaving at 400 centres, even with bathroom fixtures would then be just about adequate? Link to comment Share on other sites More sharing options...
joe90 Posted June 11, 2020 Share Posted June 11, 2020 52 minutes ago, Jml said: involved, as will a SE,. then your SE should confirm this (it’s part of his job!!!) 1 Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2020 Share Posted June 11, 2020 1 hour ago, Jml said: Many thanks for your response. BCO are involved, as will a SE,. I assume that there is some variation in actual widths of joists as have measured a few and nearer to 50 than 44? But being 44 and c16 makes sense. Bolting the existing ceiling joists with others c24 44x 170 But leaving at 400 centres, even with bathroom fixtures would then be just about adequate? It is about depth of joists when you do large spans, not width. Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 11, 2020 Share Posted June 11, 2020 Are there any underlying intersecting walls which can assume some of the loads? Link to comment Share on other sites More sharing options...
Jml Posted June 11, 2020 Author Share Posted June 11, 2020 1 hour ago, joe90 said: then your SE should confirm this (it’s part of his job!!!) None appointed as yet, as funds are very tight, trying to establish easiest, simplest therefore the most cost effective way to do things first 48 minutes ago, PeterW said: It is about depth of joists when you do large spans, not width. Ok, so probably would need deeper joists. I assume that the current ceiling joists can stay in situ. 32 minutes ago, Nickfromwales said: Are there any underlying intersecting walls which can assume some of the loads? Total span is actually over 6m but there is a structural 100mm block wall 2.4 m from one wall and 3.93m from the other on which 2 independent sets of ceiling joists rest. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 11, 2020 Share Posted June 11, 2020 A basic drawing of the existing layout would help, but here were just procrastinating as the SE and BCO will dictate what you need so as to issue the relevant certification Remember if you want to get some extra cheeky head height you could go to doubles up smaller joists and make them Flitch beams. 1 Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2020 Share Posted June 11, 2020 14 minutes ago, Jml said: None appointed as yet, as funds are very tight, trying to establish easiest, simplest therefore the most cost effective way to do things first Ok, so probably would need deeper joists. I assume that the current ceiling joists can stay in situ. Total span is actually over 6m but there is a structural 100mm block wall 2.4 m from one wall and 3.93m from the other on which 2 independent sets of ceiling joists rest. What is the span the opposite direction...? and is the ceiling coming down..? Link to comment Share on other sites More sharing options...
Temp Posted June 11, 2020 Share Posted June 11, 2020 If you have the headroom it might be better to work out how tall the new joists would need to be if the existing ceiling joists don't carry any of the load. Then put the new ones in 1" above the top of the plasterboard. Dont bolt them to the existing joists (except perhaps at the ends). That way there is no new load on the existing joists and fewer cracks in the plaster in rooms below 1 1 Link to comment Share on other sites More sharing options...
Jml Posted June 12, 2020 Author Share Posted June 12, 2020 On 11/06/2020 at 15:50, Nickfromwales said: A basic drawing of the existing layout would help, but here were just procrastinating as the SE and BCO will dictate what you need so as to issue the relevant certification Remember if you want to get some extra cheeky head height you could go to doubles up smaller joists and make them Flitch beams. Drawing attached, pitched roof with pitch running top to bottom of photo, top shows section at points AA. Link to comment Share on other sites More sharing options...
Jml Posted June 12, 2020 Author Share Posted June 12, 2020 20 hours ago, PeterW said: What is the span the opposite direction...? and is the ceiling coming down..? Span in opposite direction 4560mm as in drawing in above post. Ideally ceiling not coming down. 12 hours ago, Temp said: If you have the headroom it might be better to work out how tall the new joists would need to be if the existing ceiling joists don't carry any of the load. Then put the new ones in 1" above the top of the plasterboard. Dont bolt them to the existing joists (except perhaps at the ends). That way there is no new load on the existing joists and fewer cracks in the plaster in rooms below Ceiling height a bit tight, depending depth new joists, but that sounds like a good plan, perhaps along with 20 hours ago, Nickfromwales said: Remember if you want to get some extra cheeky head height you could go to doubles up smaller joists and make them Flitch beams. Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 12, 2020 Share Posted June 12, 2020 13 hours ago, Temp said: If you have the headroom it might be better to work out how tall the new joists would need to be if the existing ceiling joists don't carry any of the load. Then put the new ones in 1" above the top of the plasterboard. Dont bolt them to the existing joists (except perhaps at the ends). That way there is no new load on the existing joists and fewer cracks in the plaster in rooms below Issues with not being able to fit noggins ? May have to fit thicker beams to compensate. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 12, 2020 Share Posted June 12, 2020 30 minutes ago, Jml said: Ideally ceiling not coming down. Oh, that makes it interesting! Link to comment Share on other sites More sharing options...
PeterW Posted June 12, 2020 Share Posted June 12, 2020 Just looking at the Engineers drawings ... It shows collar ties at about 1.3m high by my calculations. Are there purlins down the sides and are you adding a dormer as you only have about 1m or so with decent headroom Link to comment Share on other sites More sharing options...
Jml Posted June 12, 2020 Author Share Posted June 12, 2020 1 hour ago, Nickfromwales said: Oh, that makes it interesting! Is not taking ceiling down practical? 1 hour ago, PeterW said: Just looking at the Engineers drawings ... It shows collar ties at about 1.3m high by my calculations. Are there purlins down the sides and are you adding a dormer as you only have about 1m or so with decent headroom They are my CAD drawings. Correct 2 collar ties at AA for purlins down each side. Was hoping to have a bathroom in there, but agreed decent headroom a bit sparse! Link to comment Share on other sites More sharing options...
Jml Posted June 19, 2020 Author Share Posted June 19, 2020 On 12/06/2020 at 14:07, PeterW said: Just looking at the Engineers drawings ... It shows collar ties at about 1.3m high by my calculations. Are there purlins down the sides and are you adding a dormer as you only have about 1m or so with decent headroom The bathroom idea has been abandoned, on the basis of cost and practicality. We will probably just use the room for storage. Can the 2 collar ties easily be removed or is it best just to duck under them? Link to comment Share on other sites More sharing options...
PeterW Posted June 19, 2020 Share Posted June 19, 2020 Without seeing them and how they are attached, I would expect that these are tying the purlins together to stop them bowing. Got any photos..? Also, where are the stairs going..? Link to comment Share on other sites More sharing options...
Jml Posted June 20, 2020 Author Share Posted June 20, 2020 23 hours ago, PeterW said: Without seeing them and how they are attached, I would expect that these are tying the purlins together to stop them bowing. Got any photos..? Also, where are the stairs going..? Photos of collar ties There is a door through which the photo was taken which will lead to the stairs. They are proving difficult to plan, however, hence I have another thread asking for ideas on these . Link to comment Share on other sites More sharing options...
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