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Old 25th May 2017, 02:12 PM   #1
Chris Kenefick
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Join Date: Sep 2008
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Default Lateral frame

I'm after some help here, we do a lot of domestic extensions were the clients request that the rear of the house is removed at lower level to open up the existing dwelling into the extension, normally we leave at least 1/3rd of the masonry retained to conform with Approved Document A - there's a significant number that are now asking for the whole of the rear to be removed.

My understanding is that there would be a need for 'lateral frame' to be installed to allow this, which would in essence leave two small columns to the ends of the inserted beam[s] is there anyone that knows of a way to do this to leave a flush finish IE. remove the columns to allow flush finishing of Kitchen units etc., ???

Thanks in anticipation
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Old 6th August 2019, 09:46 PM   #2
sequence_81
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Default Re: Lateral frame

Column will be needed for either or both for lateral stability (wind load) or to transfer beam load down to foundations as wall is too weak or not enough bearing. You could push the columns into the wall make up, however you need to be careful of cold bridging and depends of if cavity or solid walls, thickness and many other factors.

If purely for load transfer then re-building existing brickwork and sticking new extension wall to existing to help spread out the load would be one way. Be careful of existing foundations and their bearing capacity though. If to act as a frame due to wind load then you could possibly get away without columns if you can justify diaphragm action to transfer load down to foundations.
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Old 7th August 2019, 10:27 AM   #3
motorphotos
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Default Re: Lateral frame

As sequence 81 said the columns are intended to provide lateral restraint on the old wall line to take the lateral loads (wind load) as well as the vertical loads - as the existing rear wall is being removed the corners will be disturbed and the columns can go on the inner leaf line with the existing / new inner leaf built into the web and minimizes the outstand of the column - I would normally take the outer flange of the column into the cavity only sufficient to get the inner leaf into the web

With extensions the new cavity width will probably be 100 - 125 and will be wider than the existing so this column also hides the difference in cavity widths

Check the structural engineer august 2019 edition in Verulam there is an article by Andy Greenwood (I have no association with Mr Greenwood) which shows a diagram showing the wind load on a frame.

The other problem is the vertical load as the whole load that was spread along the existing rear wall foundation is now concentrated on the two columns so its highly unlikely that the existing foundations would be adequate so new pad foundations would be required. Consider a box frame with a head and base beam and the two columns each end - the base beam is bedded on the existing foundation full width of the building which will distribute the loads back along the existing foundation line (more steel but in most cases no foundation issues)

depending on the layout of the property the other option would be to bond the extension cavity wall to the existing to form a continuous wall but then watch the length of wall this creates between walls providing lateral restraint as this could end up too long between restraints - also its important to bond the new wall to the existing to form a continuous wall - I have had instances where despite being noted and with explicit notes about no using wall starters at the junction I have been called to site only to find a vertical joint between the new and existing - also this does not get over the difference in cavity widths

hope this helps

regards

motorphotos
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