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beko 01-30-2010 10:13 PM

Removing spine wall
 
Dear all,

I was asked to have a look at a friendís house to give them my opinion on whether it would be o.k. to take out a wall to open up their kitchen into the sitting room.
It is a semi detached bungalow with finished basement. The living area with wall removed would be Approx 20 ft wide x 20 ft long. I think the house is over twenty years old.

In a previous renovation they removed 15ft of the wall from the gable end and built a beam over, approx 1ft deep.

I looked in the attic space and there are ten trusses, 2ft apart, spanning approx 36ft front to back. I assumed the trusses would be simply supported on the exterior walls and the spine wall would be completely independent of the trusses and ceiling. I told them to go ahead, remove the wall and not to worry. Then I went home and woke up in a cold sweat. What if the roof trusses settled over time? What is the likelihood of the spine wall becoming a prop for the ceiling and roof trusses?
In that case, I imagine that when the spine wall is taken out the roof trusses would settle down further and the ceiling will start cracking.

I panicked and recommended on second thoughts that they do not remove the spine wall. I just don't understand what load is being carried. Is the spine wall a prop? Is the spine wall taking wind load and providing wind bracing? If the wall is removed and a beam is put in to replace it, will the truss load be altered, either by increased contact or reduced contact? Will load redistribution cause settlement and movement resulting in cracking in any event? If a new beam was inserted over the spine wall, then a new nib would have to be constructed to support the beam at the party wall end, assuming that it's not possible to support a new beam in a party wall. Will the nib need to be supported below in the basement and possibly need a foundation?

I have no idea how roof trusses settle over time and whether they do in fact settle onto spine walls. There is a stipple ceiling and I didn't know what tell tail signs to look for settlement. I can only imagine that over time the trusses do get used to being propped and then removing it would be to induce further settlement. I'm presuming that the trusses are designed to settle in the first place, so would it be standard to keep a gap at the top of the wall and the trusses? But what about the beam that was inserted when the part wall was removed. Would that be likely to have a gap or be tight up against the trusses. I have no idea of what happens or what is even likely. Worse case scenario; What would the degree of cracking be if the wall was removed? I feel like a dream killer. I am torn thinking taking out this 5ft section of wall would end up being more trouble than its worth and potentially causing cracking in the ceiling and expensive and troublesome remedial work. I would also be extremely interested in the kind of costs potentially involved. Or am I over reacting?

Yours torn and troubled,
Beko.

jlhaslip 01-30-2010 11:07 PM

They should be asking a Structural Engineer that question.

beko 01-31-2010 12:30 AM

I am a structural engineer by training. But I have no experience tracing loads in timber roof trusses after they have settled and I'm not familiar with domestic building construction in North America. Is there typically a gap at the top of the spine walls to allow for truss deflection? Also I'm rusty and sleep depraved since I've stayed at home mothering.
I surprised myself at how worried I got about what might happen if the wall is removed and the trusses settle further. I don't know how to calculate that either. I think hindsight is the very best teacher and would love to hear from someone with the experience of removing a spine wall. Did the ceiling crack? Was it difficult to repair?
Thanks,
Beko.

jlhaslip 01-31-2010 01:22 AM

Quote:

timber roof trusses
As in a Timber Frame? or standard 2 by material?
Are they planning on continuing the supporting beam to a full 20 feet?
I'm getting an un clear picture of the scope of the project now.
Why did they need the 15 ft beam on the previous reno?

Can you provide a sketch of the roof layout and wall layout, please.

oh'mike 01-31-2010 06:29 AM

Beko--I respect the way you are worried. You are right,the trusses should be self supporting,however I have seen trusses that sagged--

In one case with a 1970's house the builder made his own trusses---He did not know what he was doing--the sag was almost 3 inches.

That is the exception--most times the spine wall can be removed with out issue.

You might want to cover your bottom by getting an engineer in there that is up to speed on residential truss work.

Best to be cautious--Mike--

beko 01-31-2010 05:05 PM

Thanks jlhaslip and Milke,

Standard trussed rafters with nail plate connectors and longitudinal bracing, discontinued at separation wall. All the timbers look like 2x4ís.
I made a few pencil sketches; part ground floor plan, roof plan and section showing typical trussed rafter, but won't be able to scan them until tomorrow afternoon. Please come back and take at look at them and see what you think then.

Sorry for confusion. I was wrong the kitchen spine wall is ten feet long (9'8" to be precise). That means only half the spine wall was removed in a previous renovation. I don't know why they put a beam in over the part of the spine wall that was removed. Itís approx one foot deep and the same width as the kitchen spine wall. Is it possible they cut out the opening and left the top of the wall in place to avoid making a ceiling repair and that it's not a beam at all?

I will for sure pass on these good people to an experienced structural engineer. I simply don't have the practical on-site experience or the nerves to attempt to do it myself. But I feel I have to give them some idea of what seems likely and point out what might potentially be a problem. Then they can make a decision whether to go ahead and hire an expert.

Thanks again,
Beko.

beko 02-01-2010 08:45 PM

Having trouble sending attachments because I exceed the file size limit. Will try and figure out how to fix this and send again later. Please let me know if you know how to reduce a file size..

Thanks a million,
Beko.

jlhaslip 02-01-2010 09:15 PM

open them in MS Paint and scale them down to 640 x 400 pixels

beko 02-02-2010 12:39 AM

1 Attachment(s)
Thanks jlhaslip.
Ground floor plan attached

Two more to follow.

Beko.

jlhaslip 02-02-2010 12:43 AM

Are the roof trusses going left to right?

beko 02-02-2010 12:57 AM

1 Attachment(s)
Truss elevation attached. Sorry it's sideways. I don't know the actual slope of the rafters, but this gives an idea of the specific type of trussed rafter.

One more to follow.

Beko

beko 02-02-2010 01:09 AM

1 Attachment(s)
Roof plan diagramatic attached, showing the line of the trussed rafters and the separation line with the adjoining property.

Hope you can get an idea from these sketches jlhaslip. Appeciate your looking and if there is anything that would aid clarity please let me know.

Thanks a million.

Beko.

beko 02-02-2010 01:15 AM

Hi jlhasliip,
No the trusses are not going left to right. They go from top to bottom, parallel to adjoining property.

Thanks,
Beko.


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