Structural Opening – Knocking Two Rooms Into One and Fitting a Steel RSJ

By Kirk Smith

When we consider a structural knock through or opening in a wall, the procedure is not so different to perhaps creating an opening in a wall for a new window or door. But, this does not mean that the materials will be of the same specification as each individual job will possess its own structural requirement.

Is The Wall A Load Bearing Wall?

The first thing to be determined is whether or not the structure you plan on altering is load bearing or not. It will be necessary to carry out some elementary checks to know for sure whether it is load bearing or not.

Just Exactly What Is A Load Bearing Wall And How Do We Deal With It?

If a wall has any other structure above it or load as the case may be then we can consider this wall to be load bearing and as such will need to accommodate any necessary support when removing any part of it. It is quite common in many houses for dividing walls to carry the load of the first floor joists. They will therefore need some sort of support before any alteration can be made.

Supporting the load is commonly achieved by the use of steel acrow props which are inserted into the wall alongside timber needles to offer support whilst removing part of the structure.

How To Tell If A Wall Is Non Load Bearing

If the joists run at right angles to the wall then it is almost certainly carrying a load from first floor level and provisions will need to be put in place to support the load. If the joists run parallel to the wall then it is unlikely the wall is carrying any timber joists etc, but may however, still be carrying another load. You can clarify this by making some inspection holes at ceiling level and also going upstairs to see if you can see what runs on top of the wall.

For most room opening jobs or knock through’s though, you will be making your opening at a height of around 2.5 metres leaving a about 0.5 metres from the ceiling so in any case, there will still be a load to support.

The Process Of The Knock Through

OK, so we will assume that you now know the load bearing status of the wall so you can now start to prepare the job ahead. You will need to check some basic things first. Are there any heating appliances on the wall that need taken off? Are any electrical sockets in the way? If they are, you will need to get your plumber and electrical contractor to ensure any wiring or plumbing changes are carried out prior to the work being commencing.

Structural Calculations Are Vital

Prior to any structural modification you must have the load calculated by either a capable builder or preferably a structural engineer. Each job is different and may warrant a different set of rules to accommodate different loads of a structure. Typically on a domestic single leaf knock through with perhaps a 2 metre opening in a load bearing wall, a steel RSJ would be put in place to take the load above. The dimensions of this RSJ will vary and in all cases must adhere to current building control, who in all cases will want to inspect any such structural alteration. If you are in doubt at any stage of the job, you should contact your building officer for help and guidance. Remember, they are there to help you.

The Initial Stages Of The Structural Alteration

Mark the area out on the wall to reflect the opening you are planning. Additionally, mark out the where the supporting RSJ or lintel will go. The RSJ should lay on a concrete pad stone and have a minimum 6 inch bearing on each side of the wall opening. With a lump hammer and bolster, chop out the plaster from the wall to show the brickwork beneath. Repeat this procedure on both sides. Now make holes in the wall, for every metre, above where you will be positioning the steel RSJ. It is in these holes that you will place your needles which are held up by acrow props. These props will take the weight of the structure until you get the steel RSJ in place. Clean your work area and prepare any necessary platform to make your work easier for when it comes to lifting in the steel RSJ. Fitting the RSJ will need a minimum of two strong men. You will also need to ensure the RSJ has fixing points to fix your plasterboard to afterwards when making good the plasterwork and alteration.

The RSJ should be on pad stones with 6 inch minimum bearings either side and bedded on a firm mix or sand and cement at a ratio of 3:1. Once the steel is in bedded you must check for level and plumb and when satisfied build up the brickwork from on top to make a tight fit between existing brickwork and steel RSJ. Use slate to pack in and close any gap.

You should leave any supports in place until the next day or when the mortar set hard. After this point it will be safe to take them out. Afterwards, fill in the holes you made for the timber needles with leftover bricks and point up and pack in tight with slates.

The process of carrying out any structural modification should only be undertaken by a fully competent and experienced builder. All structural works should have loads professionally calculated before any part of a structure is removed. If In any doubt, contact your local building inspector for help and support.

Kirk Smith’s company 4K Construction are professional builders from Liverpool, Merseyside, United Kingdom. Please visit
4K Constructions Builders Talk for professional help and advice on construction, DIY, and all aspects of building.

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