Arun Associates Blog

Removal of load bearing walls and forming structural openings and the Party Wall etc Act 1996

Many people wish to create more space by providing structural openings in loadbearing walls of their properties.

Before one commences any work, it is important to survey the wall and area to be opened up, to assess the loads being carried from above, which could be from upper floors, ceilings, roof structure, chimneys, self-weight of masonry, and whether there are any party structure implications. All the transfer of loadings and the stresses involved need to be ascertained carefully before any work commences. Building Control may also be relevant if structural works are to be done, and a need for structural calculations and Building approvals.

If the property is listed, then no work should commence until all the necessary statutory approvals are in place from English Heritage, and perhaps, conservation officers. In some cases, planning approvals may be required, where, for example, there might be a change of use of the premises. ‘The Construction (Design and Management) Regulations 2015’ might apply, so the designer of the work needs to inform the client about those regulations at the appropriate time. Note that the ‘CDM 2015’ Regulations now applies to domestic property works, as well as other non-domestic work.

One has to ascertain whether carrying out the structural work impacts upon The Party Wall etc Act 1996 or not. If so, there will be a need and requirement to serve Party structure notices on adjoining owners under the Act.

Some may be surprised at this last point, but if foundations need enlargement or modification, or are affected in some way and near to adjoining property, there could be, in some cases, a need to serve a notice in advance of the works. Eg under Section 6 of the Act.

In forming a structural opening to a load-bearing wall, one is transferring the loads around the opening to the piers, jambs, or remaining walling wither side of the opening via some form of a structural beam, usually in steel or sometimes concrete. Before this is implemented, it is prudent to obtain professional advice in respect of the impact this alteration will have on the remaining structure, particularly if it is an older property.

Where the opening to be formed is very large, the loads and stresses transferred to the remaining brickwork and masonry may be too high for that brickwork, and overstress it, even with using padstones at the bearings. However, there is a solution to this, discussed later on.

There are different ways of transferring the loadings safely, and the intention is to avoid undue stress onto the remaining structure, avoiding cracking, crushing of masonry, or distortion of the structure. Any beams must be installed in such a way that they are physically connected to the supporting masonry, and the loads are spread as evenly as possible.

Before this is done, the loads above the new beam position need to be transferred to temporary supports.

This is done by cutting pockets in the wall above the beam position, and putting through steel or stout timber ‘needles’, ie temporary support beams, These are then supported either side of the opening with vertical struts, ‘Acrow’ adjustable props, or steel stanchions. Temporary props need to be on scaffold boards or spreader plates to avoid heavy concentrated loads.

One common problem is that the loads from the temporary supports are not adequately spread evenly to the structure below. The loads need to be transferred to a sound, relatively thick, oversite concrete floor slab, in good condition, via spreader plates. If the work is to an upper-level floor, then the temporary loads need to be transferred vertically down through the structure possibly through several floors, aligning the vertical supports and spreading the loads at floor and ceiling lines. Setting this out carefully beforehand is essential.

If the oversite concrete taking the temporary loads is thin, has voids underneath, weak pockets of subsoil underneath, or building services in that position, then serious problems and failure could occur as a result. Therefore, it may be prudent to drill, or to excavate carefully, a trial hole for investigation, to ascertain the thickness of the concrete, hardcore, and soil, and to check for any building services, eg pipes, drains, and cables, in the area. This process also helps to satisfy the establishing of existing key information under the CDM 2015 Regulations for health and safety of persons.

Once this has been done and the loads from above calculated, the surveyor or engineer will need to submit those calculations to Building Control and to establish if any notices or precautions need to be taken for the upper levels which might be affected by the works. Noise and dust may well be a consideration, affecting neighbouring properties or flats. Party Wall Awards, where relevant to a situation, should have some reference to these matters.

Where loads transferred from upper storeys are significant, and might overstress the remaining older, masonry at the piers and bearings, a more radical, and robust structural solution may have to be incorporated.

One method of installing the supports to the opening is to provide either a ‘goalpost’ type steel framework around the opening, or a fully framed steel rectangular structure, or ‘picture-frame’ structure, to transfer the loads from above to the foundations and ground evenly and safely. The connections can be bolted together for strength, and subject to fire risk assessments, welded on larger projects.

The picture frame steelwork would be assembled probably on site, from the individual steel sections, either H-section or I-section. The joints could be bolted or welded, but any welding would require fire risk assessments under the CDM Regulations 2015, and other legislation. It is necessary to set out the picture-frame steelwork carefully, ensure that steel members are horizontal and vertical, properly connected at junctions, and the lowest horizontal member is able to be covered by the concrete floor and finish.

The steelwork would need to be primed, with an appropriate corrosion resistant steel primer. Of course, the bottom member needs to be tightly positioned and bedded against the concrete foundation. The foundation needs to be checked to ensure it is in good condition and able to carry the load to be transferred.

This arrangement ensures the loads are transferred evenly to the lower foundation structure. If the foundation needs to have some brickwork amended above it, or removed to access the foundation, then that needs to be done. Any rebuilt brickwork on the existing foundation, which is intended to support the horizontal steel of the picture frame, needs to be in cement-mortar of sufficient strength and engineering brick quality, or alternatively, of concrete blockwork of appropriate density and load-carrying capacity.

Ensuring the main supporting steel beam is adequately tight to the masonry it is supporting, can be achieved with ‘flatjacks’ or pneumatic jacks, which can be expanded evenly, to achieve a good contact area. Some ‘flatjacks’ can be injected with resin under high pressure, to spread the doughnut-shaped rings apart, and ensure good contact and transfer of stresses evenly. This avoids gaps which might otherwise cause the supporting steel or concrete beam to settle unevenly.

These flatjacks tend to be expensive, but are ideal for larger buildings, and significant openings, such as the Westfield example given by Nick Huband, a forensic building engineer.

Hardwood timber folding wedges could also be considered to be hammered in before the beam is ‘pinned-up’ with a stiff mix dry-pack or a semi-dry pack of cement/cement-mortar. This needs to be given adequate time to set and harden before temporary props are removed.

The temporary supports and needles should be left in place for sufficient time to ensure the new beam, and supporting framework has been bedded-in, any cement mortar or ‘pinning-up’ to the masonry has set and hardened, in accordance with good practice. Premature removal of the temporary needling supports can result in deflection of the supporting beam, cracking of masonry, distortion, and even collapse, so due care needs to be taken. (The use of a simple flow chart checklist can help here, to ensure a strict procedure is followed.)

Eventually, the needling temporary supports can be removed, carefully and slowly, ensuring all loading is transferred to the picture-frame and steel beam. Finishes can then be considered to conceal the steelwork, and all necessary fire-protection provided in accordance with Building Regulations.

Neil Thind gives an example of a situation where the temporary Acrow props sank into the ground on one job inspected because the supporting steel beam was not adequately pre-stressed with the correct procedure. Uneven settlement and deflection can impose high stresses and cause serious problems, difficult to rectify, and causing cracking of finishes.

Nick Huband, the eminent forensic building engineer, speaking on the video, prefers the rectangular-framed ‘picture-frame’ solution to that of steel goalposts, which are not as rigid, due to the omission of the bottom horizontal member. In comparison, the picture-frame solution is completely framed and rigid, providing the joints are properly designed and constructed. It will, however, take slightly longer to install and be more costly than the simpler, ‘goalpost’ solution, but in many ways is more robust, and can take heavier loads to be transferred back to the foundations and soil. The goalpost solution may be more practical, however, for upper storeys which have to bridge over neighbouring properties’ openings below.

In most cases, Nick Huband advises the aim is to transfer the loadings down into the original foundations using the picture-frame steelwork and to avoid having to alter the foundations themselves.

Neil Thind, Party wall surveyor, is particularly looking at the ‘Act’ being considered, in case there might be Party-structure implications where there are adjoining owners or occupiers. It is not impossible for a poorly constructed new structural opening in a block of flats, to have a knock-on effect to another flat adjacent, or even remote from the unit which implemented the structural works. Schedules of condition before works starting are advisable, irrespective whether the situation falls under The Party Wall etc., Act 1996, or not.

If one is generally not cutting into the party wall or party floor/ceiling, as part of the intended works, then in many cases, notices under the Act are not required. (However, this is only general guidance, and some aspects of the Act go beyond Party structures, such as Section 6 works, where notices do have to be served.) The freeholder of the building may have to be served notice by the leaseholder, if structural alterations are anticipated.

Nick Huband makes the point in the video, that one should avoid as far as possible, disturbing the foundations to the party wall, when transferring loads from forming new structural openings.

Not all works described above will require Party Wall Agreements or even notices under the Act, as each situation is different. Licences for alterations will be required in many situations where the property, flat or office is leased. These will need to be formally applied for by the leaseholder, and conditions imposed will need to be adhered to. Professional advice from the outset is advisable, usually before contractors are involved.

Removing support to a party wall affects the party structure, and there may be legal implications here, under the Party Wall etc Act 1996. This needs to be addressed at an early stage in the proposed building works. Any cutting away into a party structure may trigger the Act, and require formal notices to be served.

Even if the works are outside the Party Wall etc  Act 1996, the engineer and surveyor advising the client needs to be conscious of potential damage issues to neighbouring properties arising through the works.

Schedules of condition with adequate photographs before the works start can assist surveyors, engineers and clients in dispute situations, that may arise later on.

Finally, please be aware that the above information is for guidance only, and all necessary statutory, legal approvals, party structure approvals, and licences, must be first obtained before carrying out any structural works.

Revised Dated May 2019

 

 

 

 

 

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