- Thread starter GerryC
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Hi Steve, hope I’m not testing your patience too much! After much thought ….
the most important question for me right now is this. Putting aside if its makes room usable or not … in order to postpone for a year the work involved to fully investigate and repair the problem, what straps/props/braces, if any, would you put in place that would significantly reduce the chance of further roof spread causing more serious damage. (Also bearing in mind engineer has advised at least 3 straps asap)?
RE bents / stick built frame I measured the distance from gable end wall to party wall = 15.5’ Measuring 12’ from the gable end wall ends at approx. mid-point between the right side of the window and the left side of the door (looking at front of building fm the outside).
Bearing in mind the lean in the wall seems to come back from furthest-into-the-plinth back to normal middle-of-plinth, immediately right of the door, that would seem to indicate that there may well be bent post around that point: should I remove enough plaster from the inside of the wall below the wall plate (which is already exposed on that side) to see if there is a decent sized post there?
Collar tie and removing ceiling: small hole no problem but might be better for going forward to make that into a permanent openable hatch with door so inspections in future easy? Would only need light board hatch? And if one rafter joint can go others well possible. Also on this I’m checking with neighbour who already has such a hatch of he has actually put his full body weight inside this roof space or just looked in)
the most important question for me right now is this. Putting aside if its makes room usable or not … in order to postpone for a year the work involved to fully investigate and repair the problem, what straps/props/braces, if any, would you put in place that would significantly reduce the chance of further roof spread causing more serious damage. (Also bearing in mind engineer has advised at least 3 straps asap)?
RE bents / stick built frame I measured the distance from gable end wall to party wall = 15.5’ Measuring 12’ from the gable end wall ends at approx. mid-point between the right side of the window and the left side of the door (looking at front of building fm the outside).
Bearing in mind the lean in the wall seems to come back from furthest-into-the-plinth back to normal middle-of-plinth, immediately right of the door, that would seem to indicate that there may well be bent post around that point: should I remove enough plaster from the inside of the wall below the wall plate (which is already exposed on that side) to see if there is a decent sized post there?
Collar tie and removing ceiling: small hole no problem but might be better for going forward to make that into a permanent openable hatch with door so inspections in future easy? Would only need light board hatch? And if one rafter joint can go others well possible. Also on this I’m checking with neighbour who already has such a hatch of he has actually put his full body weight inside this roof space or just looked in)
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Hello Gerry, don't worry about my patience, it's not infinite but neither is it limited when someone needs help.
- Strap Positioning - the issue here is; your need to continue using the house while stabilising its structure to prevent further damage.
- To my mind these requirements conflict with each other insofar that any sensible positioning of the essential straps will significantly inhibit/prevent day-to-day use of the bedroom in particular as the primary strap would need to run between the two posts at the front and rear and ideally near the top of the posts forming the slipped bent just below the level of the top plate.
- Has your engineers indicated just where in the frame he/she would site the suggested straps and what purpose each of these would achieve/contribute to stabilising the structure?
- I would remind you that any straps connected directly to any of the horizontal timbers in the frame runs the risk of serious damage to M&T joints the current condition of which are entirely unknown.
- Bents/Stick Built - Your measurements seem to confirm my present thinking that it's a timber frame rather than stick built. The post that has slipped off vertical would be somewhere near that 12 foot mark from the gable wall.
- Ceiling Hatch - for the future it would be useful for you to have such access to allow inspection of the roof timbers. But, some thought about its siting will be needed and getting a frame in place to support it may be problematic as it must not be linked to other timbers in the roof that may have shifted when the post slipped - you do not want to add stiffenings that may inhibit the movement of the frame back to its original position.
Hey Steve,
Re Planning: have engaged with conservation officer and they have details of the problem to be fixed and agreed strapping propping goes ahead without planning p. Have drafted planning permission but keeping on hold until we complete investigation and are more sure exactly what we will do.
Rr Temporary ‘holding’ support. I may decide to hire temporary accommodation if that’s what’s needed. But could I tie you down (as it were!) further on what you believe would be essential to put in place if I were to delay work for a year? I think you are saying that the only thing that is needed for this phase (if we do have to delay) are 2 straps placed on the floating post, one over the floorboards on the first floor (if one at ceiling level ground floor not possible) and the other at the top of the post. Other posts do not need strapping. Supports for the beams and dormer not needed until work to begin on dismantling the infills OR moving posts (replacing decayed/broken or moving back into vertical position). Is that your view?
Rr structure: to properly understand what posts there are in the wall i could remove the internal plaster just below the wall plates which are already exposed. Given the lean on which some of the time i'd be perched right on top of, would you say i'm safe to to this without any further supports to the beams / posts?
Re the engineers view …re strapping .. he said strap the wall plate and when I put it to him tenons not reliable / plate might snap/not be string enough, he said he’s done loads and never had that problem .. however he said we could strap around the plate/post joint (wrap over beam, around post and back to other side)
Re the engineers view …overall .. is that the building is poorly designed to resist roof spread (for that the collar tie should be in the lower 3rd of the rafters not the top third). So he says even if the floating post is due to broken brace/decayed sole plate/other, it makes sense to supplement the frame to future proof it (future proofing was my main brief as don’t want to have to deal with structural issue when I’m older / gone and wife on her own).
Sorry the life situation complicates the tech details.
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Hello Gerry,
Good to hear the CO is engaged and has confirmed you can proceed with the stabilisation phase and it's wise to hold the application until you have a hard plan of action ready based on on your further investigations.
I've prepared the crude diagram below to summarise the current understanding of the frames possible condition and to highlight my present thinking on a strapping plan to stabilise the building ahead of the further investigation and remedial works - more about that later.
Rr structure: to properly understand what posts there are in the wall i could remove the internal plaster just below the wall plates which are already exposed. Given the lean on which some of the time i'd be perched right on top of, would you say i'm safe to to this without any further supports to the beams / posts? Always better to be safe than sorry. If I recollect, you have already placed timber props under some of the floor joists supporting the bedroom floor. When positioning props beneath a series of floor joists a builder would typically use a scaffolding plank to span a number of the joists and position the props beneath it to spread the load from above whilst minimising the number of props needed to support the joists. The same approach can be used with a length of suitable timber that would span just two or three joists. Also, you could lay a sheet of say plywood on the bedroom floor to spread your weight over a much larger area to minimise the risk of point loads on particular spots.
Re the engineers view …re strapping .. he said strap the wall plate and when I put it to him tenons not reliable / plate might snap/not be string enough, he said he’s done loads and never had that problem .. however he said we could strap around the plate/post joint (wrap over beam, around post and back to other side) Whilst your engineer has, I assume, had the benefit of an on-site inspection I doubt that he has been able to see and examine any more of the frames condition than you have. Ordinarily I may agree with him/her that the M&T joints connecting the plates to the posts may be in a good enough condition to withstand the pressures exerted by a winch strap. However, that, to my mind, is a very big and possibly unsafe assumption to make without close visual inspection. Particularly as it ignores one of the larger, and to now undiscussed 'elephants in the room'! The exterior of your house has been coated in a render of some kind for at least 70 years. Hopefully, breathable materials and paints were, and have been used since, to maintain that render; but that too is an unsafe assumption. As a consequence moisture may have been being trapped in the frames timbers for decades. As a consequence the pegs used to lock the M&T joints together may have become a route for moisture penetration thus causing the tenon blades and sockets to rot. To my mind the only safe assumption to make at this stage is that NONE of the joints in that frame should be depended on to carry any undue load. Ultimately I suspect that you will find that a section of the sole plate has rotted out and that this is the true root cause of rafter spread.
Re the engineers view …overall .. is that the building is poorly designed to resist roof spread (for that the collar tie should be in the lower 3rd of the rafters not the top third). So he says even if the floating post is due to broken brace/decayed sole plate/other, it makes sense to supplement the frame to future proof it (future proofing was my main brief as don’t want to have to deal with structural issue when I’m older / gone and wife on her own). He/she is not wrong and better/stronger designs for the principal trusses of timber frame homes are available but few of these may be suitable for your needs. As they say, 'theres more than one way to skin a cat' and I have previously suggested how suitably designed steel plates could be used to supplement/replace the extant M&T joints at the apex of the truss and at the connections between the rafters and the posts.
Back to the strapping plan. The diagram below should be largely self-axplanatory but the red lines represent my thoughts regarding where the straps needed to stabilise the building may be best located. those at the juncture between the posts and the rafters are intended only to ensure that the foot of the rafters do not 'skip' out and the primary strap between the posts at a height just below the head of the posts is intended to resist any lateral shift of either of the posts as a consequence of say a heavy snow load. I would advise that the steel wire cable is used to to connect to a ground anchor sited outdoors to secure the foot of the slipped post to resist any further movement.
Good to hear the CO is engaged and has confirmed you can proceed with the stabilisation phase and it's wise to hold the application until you have a hard plan of action ready based on on your further investigations.
I've prepared the crude diagram below to summarise the current understanding of the frames possible condition and to highlight my present thinking on a strapping plan to stabilise the building ahead of the further investigation and remedial works - more about that later.
Rr structure: to properly understand what posts there are in the wall i could remove the internal plaster just below the wall plates which are already exposed. Given the lean on which some of the time i'd be perched right on top of, would you say i'm safe to to this without any further supports to the beams / posts? Always better to be safe than sorry. If I recollect, you have already placed timber props under some of the floor joists supporting the bedroom floor. When positioning props beneath a series of floor joists a builder would typically use a scaffolding plank to span a number of the joists and position the props beneath it to spread the load from above whilst minimising the number of props needed to support the joists. The same approach can be used with a length of suitable timber that would span just two or three joists. Also, you could lay a sheet of say plywood on the bedroom floor to spread your weight over a much larger area to minimise the risk of point loads on particular spots.
Re the engineers view …re strapping .. he said strap the wall plate and when I put it to him tenons not reliable / plate might snap/not be string enough, he said he’s done loads and never had that problem .. however he said we could strap around the plate/post joint (wrap over beam, around post and back to other side) Whilst your engineer has, I assume, had the benefit of an on-site inspection I doubt that he has been able to see and examine any more of the frames condition than you have. Ordinarily I may agree with him/her that the M&T joints connecting the plates to the posts may be in a good enough condition to withstand the pressures exerted by a winch strap. However, that, to my mind, is a very big and possibly unsafe assumption to make without close visual inspection. Particularly as it ignores one of the larger, and to now undiscussed 'elephants in the room'! The exterior of your house has been coated in a render of some kind for at least 70 years. Hopefully, breathable materials and paints were, and have been used since, to maintain that render; but that too is an unsafe assumption. As a consequence moisture may have been being trapped in the frames timbers for decades. As a consequence the pegs used to lock the M&T joints together may have become a route for moisture penetration thus causing the tenon blades and sockets to rot. To my mind the only safe assumption to make at this stage is that NONE of the joints in that frame should be depended on to carry any undue load. Ultimately I suspect that you will find that a section of the sole plate has rotted out and that this is the true root cause of rafter spread.
Re the engineers view …overall .. is that the building is poorly designed to resist roof spread (for that the collar tie should be in the lower 3rd of the rafters not the top third). So he says even if the floating post is due to broken brace/decayed sole plate/other, it makes sense to supplement the frame to future proof it (future proofing was my main brief as don’t want to have to deal with structural issue when I’m older / gone and wife on her own). He/she is not wrong and better/stronger designs for the principal trusses of timber frame homes are available but few of these may be suitable for your needs. As they say, 'theres more than one way to skin a cat' and I have previously suggested how suitably designed steel plates could be used to supplement/replace the extant M&T joints at the apex of the truss and at the connections between the rafters and the posts.
Back to the strapping plan. The diagram below should be largely self-axplanatory but the red lines represent my thoughts regarding where the straps needed to stabilise the building may be best located. those at the juncture between the posts and the rafters are intended only to ensure that the foot of the rafters do not 'skip' out and the primary strap between the posts at a height just below the head of the posts is intended to resist any lateral shift of either of the posts as a consequence of say a heavy snow load. I would advise that the steel wire cable is used to to connect to a ground anchor sited outdoors to secure the foot of the slipped post to resist any further movement.
Hey, nice summary thanks, makes sense.
One question on the strapping placement diagram: so those straps at the rafter / post join do not go across the building just wrap around the post/beam and rafter?
The anchor was a surprise. How heavy duty would the spec be for that -- 4 foot post driven into ground? Set in concrete block and buried in ground? Ive got a meeting with the Engineer on Friday to talk further re strapping and propping so will update you next week on that front.
M&T joints at the apex of the truss ... yes i'm doing to go with that, makes compete sense to me
AOB I talked with a contractor the other day and he said he would only use strong boys on acrow props to suport the whole front wall ...no needles or strapping. I hadnt heard that builders and engineers often disagree, so new to this debating chamber ... i guess for insurance purposes builders can argue with the engineers but in the end have to do what they say? Do you know?
One question on the strapping placement diagram: so those straps at the rafter / post join do not go across the building just wrap around the post/beam and rafter?
The anchor was a surprise. How heavy duty would the spec be for that -- 4 foot post driven into ground? Set in concrete block and buried in ground? Ive got a meeting with the Engineer on Friday to talk further re strapping and propping so will update you next week on that front.
M&T joints at the apex of the truss ... yes i'm doing to go with that, makes compete sense to me
AOB I talked with a contractor the other day and he said he would only use strong boys on acrow props to suport the whole front wall ...no needles or strapping. I hadnt heard that builders and engineers often disagree, so new to this debating chamber ... i guess for insurance purposes builders can argue with the engineers but in the end have to do what they say? Do you know?
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Hi Gerry,
'It's hard to explain in words and the drawing software I have is not very helpful but here goes. They are not separate straps. The 'tail' of each of the straps connecting the posts is, from inside the bedroom, passed outside the post and back indoors, it is then passed around the internal face of the post and up and over the top of the principal rafter and back down to the the main length of the strap where it is tied off. The two lengths of the strap between the posts are then connected with a winch and tension is applied. The loop over the rafters provides a compressive force that will prevent the rafters 'skipping out'. Be aware though that this strap should not be used to pull the frame back to vertical - that's the job of a winch located outdoors and connected to a ground anchor.
There are various types of 'ground anchor' and the choice will depend on the nature of the ground itself and the location and depth of water, gas and electricity services to the house. I'm not thinking of anything permanent - so forget concrete - and it may be possible for you to get away with using a single (1 metre) steel spike driven into the ground at, say, a 45degree angle. Alternatively, you could use 'auger type anchors that in effect are drilled into the ground, again at an angle. Remember, the first objective is to prevent further unwanted slippage of the post. However, the same ground anchor arrangement will be needed to pull the post back to vertical when all the preparation work is completed - that post is the principle actor (the biggest lever you have) to achieving the final goal.
AOB - Builders, engineers, architects, et al often disagree over some of the details and oftentimes it's fairly meaningless and unimportant to you and I. The choice of tools is larergly up to the contractor but I would expect them to follow any professional guidance when sensible to do so. In this case 'strong boys and acrow props' will do exactly the same thing as a needle prop. The key issue is that these should not be used for anything other that support for the structure - they must not be used to provide 'lift'.
'It's hard to explain in words and the drawing software I have is not very helpful but here goes. They are not separate straps. The 'tail' of each of the straps connecting the posts is, from inside the bedroom, passed outside the post and back indoors, it is then passed around the internal face of the post and up and over the top of the principal rafter and back down to the the main length of the strap where it is tied off. The two lengths of the strap between the posts are then connected with a winch and tension is applied. The loop over the rafters provides a compressive force that will prevent the rafters 'skipping out'. Be aware though that this strap should not be used to pull the frame back to vertical - that's the job of a winch located outdoors and connected to a ground anchor.
There are various types of 'ground anchor' and the choice will depend on the nature of the ground itself and the location and depth of water, gas and electricity services to the house. I'm not thinking of anything permanent - so forget concrete - and it may be possible for you to get away with using a single (1 metre) steel spike driven into the ground at, say, a 45degree angle. Alternatively, you could use 'auger type anchors that in effect are drilled into the ground, again at an angle. Remember, the first objective is to prevent further unwanted slippage of the post. However, the same ground anchor arrangement will be needed to pull the post back to vertical when all the preparation work is completed - that post is the principle actor (the biggest lever you have) to achieving the final goal.
AOB - Builders, engineers, architects, et al often disagree over some of the details and oftentimes it's fairly meaningless and unimportant to you and I. The choice of tools is larergly up to the contractor but I would expect them to follow any professional guidance when sensible to do so. In this case 'strong boys and acrow props' will do exactly the same thing as a needle prop. The key issue is that these should not be used for anything other that support for the structure - they must not be used to provide 'lift'.