![]() ![]() Cavity InsulationĬlipped onto the wall tie in the diagram, is an insulation retaining clip. A useful book covering is the BDA Guide to Successful Brickwork available on Amazon. The cavity can then be enlarged to 100mm.īoth skins of the wall must be at least 90mm thick for this. The exception to this, is when vertical twist ties (second image above) are used and spaced at 750mm horizontally. This does not apply if the cavity skins are bonded together.Ī cavity must be between 50mm and 75mm wide, with these figures as a minimum and maximum width. These ties should be placed at 900mm centres horizontally, and 450mm vertically.Īt any openings, the ties should be placed with at least one tie, for every 300mm of height and within 225mm of the opening. Severe exposure is defined in the BS, but to be on the safe side, almost all ties these days are made from stainless steel or are galvanised. In that case, stainless steel or non ferrous ties should be used. 5628 1978 the specification for metal ties for cavity walls excepting conditions where severe exposure may occur. Secondly, the wall ties themselves have a kink, twist or tail, which allows water to form on this part of the tie and, given that water cannot run uphill, drip off the lowest point.Īll wall ties should comply with BS. To counteract this, firstly it is important they are installed "on the level" or even sloping toward the outside of the building. If the wall tie, which is built into the joints of the masonry, is placed so that it slopes down toward the inner skin of the building, water can run down it and soak into the inside wall. An important function, but from a damp point of view, sometimes a dangerous one. The first thing we see as we go up the cavity is a wall tie, this is necessary to "tie" the two halves of the wall together and stop one moving independently of the other. At the bottom of every cavity is a foundation of some kind, this will be dealt with in another project which will include a ground floor slab construction. We will start at the bottom of the diagram and explain. That is the two leaves, or skins, of the wall have to be connected. Or a number of reasons that we will explain below, the cavity has to be bridged. By inserting a cavity, that scenario is impossible. Without a barrier of some kind, there is a chance that water will work its way indoors, however thick the wall. Most masonry is porous to some degree, and sooner or later, especially with weak, or incorrectly constructed joints, that masonry will let in water. The cavity wall was introduced into buildings because it is the greatest of all damp precautions, water cannot travel across a void. Not all of this goes into each cavity, but we have put everything into one to make it easier to understand. If you have enough load bearing wall height above an opening, the "arch effect" of masonry actually reduces the load on a lintel above an opening, but that requires an engineer to save the money invested.The diagram below shows a cavity in all of its glory. If your window opening is NEW and is 48" wide, you may have to do some investigation yourself (drill, probe, etc.) IF you know what to look for. If you are looking at other construction, the flat bar running horizontally may just be a plate that si there to support the masonry above DURING construction and is supported by props that are removed later to allow the window installation. ![]() If all gets down to the dimensions (thickness, wall height, wall length, wall section height above openings) and a simple answer will not be possible without it. Bond beams are usually not detailed on a plan because they are usuallt built but local conventions.Ī 6" thick block wall has tremendous strength, as exhibited by the many 7 to 20 story 6" load bearing block apartment buildings (partially reinforced and not technically reinforced on the upper 2 or 3 floors). If your building department is any good you will have a bond beam as a top course for a wall and often have a bond beam as an intermediate support/continuity an a gable end of a home.Ī better description of the wall (height, length, etc.) is needed and is the reason you will never get a firm answer to your question without it. Its purpose is not really structural, but provide a solid bearing surface for any construction above (more floors or roof trusses). A bond beam usually the top course (or two ). ![]()
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