# Forum Home Renovation Roofing  Removing Collar Ties

## LindaC

I am looking for a way to *remove 4 Collar Ties* in the roof space so it an be used for storage. 
Ours is a small, ground level, rectangular cavity brick house with a hipped tiled roof built in 1943. The internal walls are single layer rendered brick with a hallway pretty much up the middle from front to back.   
Is it possible to *replace the Ties* by :  cutting thick plywood sheeting (18 mm?) into triangles that match the roof pitch, with an arched base;inserting the pieces under the Ridge; and,attaching them to the 4 sets of rafters that currently have Collar Ties.I am figuring on cutting the 'arched triangles' from a piece of ply measuring 2400 mm x 900 mm. The resulting insert for replacing the Collar Tie would measure approximately 2400 mm W x 750 mm H.  
IS THIS SCHEME POSSIBLE? ANYONE GOT EXPERIENCE WITH REMOVING COLLAR TIES??

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## Bloss

Bit hard without seeing, but your idea of using plywood bracing should be OK, and what you suggest would work, but is probably overkill. 
Collar ties are to resist the outwards spread of the rafters from the downwards forces (weight) of the roof timbers themselves and the roof covering (in your case tiles). 
To brace against those forces you could use smaller triangular or trapezoid (ie triangle with the point cut off so that the piece sits below the ridge board) piece of plywood screwed or nailed to to the rafter - say 300mm- 400mm deep and on both sides of each rafter set. 
If what you suggest provides the space you want when you place ply or other flooring over the ceiling joists then you are probably OK to place the ply in place then remove the existing ties.  
But . . . you really need to get someone to have look for you or provide some pics of the roof as there are so many variations possible in cut-in roofs you need to look at each one specifically. 
Having said all that you need to be aware that removing any part of a roof structure needs to be done by a licensed builder in all states - and for good reasons: if a mistake is made in any change there can be a rapid and catastrophic failure, or sometimes a gradual failure over time that can damage the structure. Both can be dangerous and often are costly to remedy.

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## LindaC

Oldbloss, thanks for your comments. I am not sure what you mean when you mention 'overkill'? Yes, I will get a professional in - I am just trying to do my homework first. 
To illustrate the idea, here is a drawing.   
Other questions (amongst many) are :  Would it be a more sound scheme if the trapezoids were cut out of a 3600 mm ply length?Does the arch have to be a perfect circle, or can it be more oval (to gain more head room)?Would the trapezoid inserts have to be either side of the 4 sets of rafters, or would one on each rafter set do?Do you have any idea of what the optimum ply thickness might be?I have been trawling the Internet looking for relevant information. *Can anyone suggest useful Web Sites for amateurs?*

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## Bloss

Without seeing the actual roof it is always a bit hard to judge, but by overkill I meant you wouldn't need to have the ply bracing so large. 
Other questions (amongst many) are :
Would it be a more sound scheme if the trapezoids were cut out of a 3600 mm ply length?
Response: 2400 looks fine - I think you could go to 1800.
Does the arch have to be a perfect circle, or can it be more oval (to gain more head room)?
Response: You can give yourself more headroom by ovalisation.
Would the trapezoid inserts have to be either side of the 4 sets of rafters, or would one on each rafter set do?
Response: I would put it on either side of each rafter, but that's just me. That makes that top section into a braced box section girder and if you put a few blocks in at the cut-out of your arch/oval or face the curve with a strip of glued and nailed ply (say 6mm) that would add strength and look better too.
Do you have any idea of what the optimum ply thickness might be?
Response: If you do both sides then 9mm or 12mm would be OK. 
I assume that the long strut that is marked as a dotted line is an existing support and is to be removed? Is there just one of those or one at each rafter? In any case you need to be sure that the forces it is designed to resist are accounted for in anything you do.  
In all this type of work the ideal is to put in place the new structure then remove the old and if you take a few good measurements beforehand you can quickly see if the removal is having an unintended consequence that needs attending to before proceeding further. 
BUT .  .  . as I said you should not rely on this advice alone - so getting the professionals in to have look is the go. More searches on this forum might help and the plywood association website has some good technical information too for example see:  http://ewp.asn.au/ 
and  http://www.byohouse.com.au/forum4/index.php 
and  http://www.archicentre.com.au/html/downloads.html 
As I repeated already each building or renovation site needs the guidance informed by years of knowledge of a professional, even when the actual work is to be done by a DYIer.

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## LindaC

Thanks Oldbloss for the Web Links - I expect a few hours of my day will disappear chasing their information (hooray for/damn those computers?!). 
The broken line indicates the roof line for a small gable. This is over the Loungeroom that extends out 1.5 m from the front line of the main rectangle of the house plan. I have done a scale drawing of the house showing walls, ceiling joists and roof, but I can't make it small enough to post here. 
I have realised that the elevation drawing posted doesn't show the hallway wall - which is a significant structural consideration. It is 100 mm thick brick that I should have drawn 1300 mm (in scale) to the left of the 'middle' wall shown in the drawing.

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## DvdHntr

You should install hanging beams at the location of the collar ties and strengthen the rafters at either end.

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## Bloss

That's why LindaC needs to have a professional look at the actual work needed - as she intends to do. 
If, as the diagram seems to indicate and her clarification suggests, there are two internal walls supporting the ceiling joists and all she is doing is using the area for storage space then hanging beams over strengthened rafters would not be needed. 
A professional should also tell her her what sort of loads she can expect to put into storage up there, but it would be unusual (although not unheard of - folk do some funny things) that any items would impose a load heavier than the weight of a single person (say 100Kg) kneeling or standing on a single joist - which can easily manage such a load and more. 
If, as is likely, the space is floored using 19-20mm panelfloor or plywood to the edges of the accessible area the existing joists should easily carry the loads imposed without any additional beams or rafter strengthening. 
I know it appears self-evident, but the advice on forums should always be taken as being in the nature of general guidance (albeit possibly from expert and experienced members). But there is no real way for a novice in a particular area to easily know what advice being proffered is properly underpinned by appropriate knowledge and what isn't. 
There are local, state and national rules governing most of the work proposed (and about complying with the BCA), but most forum members are simply getting as informed as they should before proceeding. 
As LindaC knows this is not a game for novices acting alone and she has said she will be getting someone in - she now has some more information on which to base any discussions with that adviser.   :2thumbsup:

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## DvdHntr

As soon as you remove the collar tie you need to replace it with a support at the same location.

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## Bloss

As I said in my second post: 
"In all this type of work the ideal is to put in place the new structure then remove the old and if you take a few good measurements beforehand you can quickly see if the removal is having an unintended consequence that needs attending to before proceeding further." 
Not just ideal - pretty much mandatory for DYIers. In this case one would put put up the plywood bracing on one side of the set of rafters with the collar-tie then remove the tie then put up the next piece of ply and finish off. Then do the next rafters with ties in the same way. 
LindaC's professional adviser will tell her that stuff anyway would be my guess.

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## DvdHntr

> As I said in my second post: 
> "In all this type of work the ideal is to put in place the new structure then remove the old and if you take a few good measurements beforehand you can quickly see if the removal is having an unintended consequence that needs attending to before proceeding further." 
> Not just ideal - pretty much mandatory for DYIers. In this case one would put put up the plywood bracing on one side of the set of rafters with the collar-tie then remove the tie then put up the next piece of ply and finish off. Then do the next rafters with ties in the same way. 
> LindaC's professional adviser will tell her that stuff anyway would be my guess.

  But the plywood brace will not restrain the rafter at the same point as the collar tie currently does. As long as she gets a professional to give her the right advice.

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## Bloss

> But the plywood brace will not restrain the rafter at the same point as the collar tie currently does. As long as she gets a professional to give her the right advice.

  That's right it will retain it at more points creating a truss from the rafters (if done in the manner I described) and in fact be stronger than the collar tie. 
As you say - all to be confirmed by LindaC's builder rather than through further chest banging in this thread . . .

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## Vernonv

> ...rather than through further chest banging in this thread . . .

   :Confused: Why do you seem to want to shut down discussion in this thread? I would have thought the more input that LindaC gets, the better (I'm certainly interested in other peoples thoughts and ideas on the subject). I think the comment says more about you than any of the other posters. 
Keep the comments rolling in I say ...

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## LindaC

*DvdHuntr :*
I am not sure what you mean by - 'You should install hanging beams at the location of the collar ties and strengthen the rafters at either end.' 
Are you talking about a hanging beam across (90 deg angle) the ceiling joists with a Knee Wall (purlin under the rafters with struts to the beam) to support the rafters?  *Sister Rafters* 
I have discovered another configuration in a book.  This shows the plywood 'trapezoid' gusset under the ridge and 'Sister' Rafters fixed to the existing rafters.  It is probably not relevant to my roof because they were actually talking about fixing sagging rafters, but I wondered about it. 
Would doing this be a waste of time, or a bit of overkill?  
Brian the Builder is coming tomorrow to look at the job.  I'll let you know next week what his opinion is.
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## DvdHntr

Just like the purlin you have noted. It must be a much deeper section though as it is transferring that horizontal load.

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## LindaC

Brian the Builder has visited.  There is still some debate about exactly what to do with the collar ties.   
Other significant issues are about installing : Lining Under the Rafters;Insulation;Ventilators - Or Not.I am going to start another Thread about that.  The considerations are : There is some natural ventilation through the tiles.  Lining and insulating the rafters would block the existing air flow. Being a tiled roof, it is not tied to the external cavity brick walls.  Would lining the rafters, thus sealing the roof space, alter inside/outside air pressures, and increase the chance of the roof being blown off in extremely strong winds? There aren't any Overhangs/Eaves.  A ventilator would need fresh air input to function successfully - would vent panels have to be installed in each room's ceiling?
I will post to this Thread final details about what happened in the roof space.

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