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Raising Party Walls in timber

PARTY WALL etc ACT 1996 Section 2(2)(a) 

Raising of party walls

In the aftermath of the Great Fire of London in 1666 the Authorities legislated to prevent a re-occurrence of the catastrophic damage by requiring future construction to be built in masonry.  Until the repeal of the London Building Acts an owner wishing to raise a party wall was obliged to do so in brickwork or stonework and furthermore to do so above the roofline as a parapet.  Apart from the fire-resisting qualities parapets provide a harmonious architectural addition to terraced properties. 

Some building professionals interpret the London Building Act requirements as a precedent for party walls to be raised in masonry; however, others take the view that modern materials enable the wall to be raised in clad timber framing. 

When applied to loft extensions Planning Authorities have differing interpretations of Permitted Development rights. The Law of Property Act defines a party wall as a wall jointly owned, severed vertically at the centre line but with the benefit of easements of support. The Planning Acts neither define party walls, boundaries nor curtilage, thus when considering whether raising the full width of a party wall as part of a loft extension is Permitted Development, the law is unclear. In 2000 the London Borough of Enfield refused an application to certify Lawful Development for a loft conversion, the dormer cheeks of which were raised the full width of the party wall. The refusal was on the grounds that the development was beyond the curtilage of the subject house and therefore not Permitted Development. On Appeal the Inspector disagreed with the Council on the grounds that the curtilage had to include the full width of the party wall, without which the house would be incomplete. A similar decision was reached in 2009 against the London Borough of Barnet. In 2010 the Court of Appeal, quoting the Oxford English Dictionary, held against the London Borough of Waltham Forrest that the curtilage of a dwelling house included the full width of the party wall. Planning Decisions are not binding; however there appears to be a consistency in the decisions from which it is reasonable to suggest that a party wall falls within the curtilage of a building. Regrettably many Local Planning Authorities disagree, leading to curious construction techniques and differences in the interpretation of Section 2(2)(a) of the Party Wall etc Act. 

An important purpose of the Party Wall etc Act is to prevent a Building Owner from causing unnecessary inconvenience to an Adjoining Owner. The question to be answered therefore is “can the raising of a party wall be achieved in materials other than masonry and meet the objectives of the Act without causing unnecessary inconvenience?”

The Building Regulations permit the construction of timber framed party walls. 
The raising of a party wall in brickwork is arguably the best way of achieving a satisfactory aesthetic appearance and fire-resistance, but it has to be acknowledged that a 112.5mm or 225 mm thick brick wall is neither waterproof nor sufficient to comply with today’s requirement for energy conservation.  Siting of efficient damp proof courses can also be challenging.

There are few, if any, grounds to challenge notices to raise a party wall in masonry and access to carry out that work.  Importantly the raising in masonry of a party wall facilitates the ability of both owners to subsequently raise the wall. Thermal insulation can be provided internally and if properly detailed the wall can be raised as a parapet thereby enabling a waterproof junction between flat or pitched roofs and the parapet.  The Adjoining Owner can subsequently enclose upon the raised party wall and pay half the costs at the current price.

With the need to increase living space owners are resorting to adding loft rooms, the cost being significantly less than moving house and the process is made easier by relatively relaxed Planning policies. To fulfil significant demand Loft building companies are starting up everywhere, some employing designers with inadequate knowledge of sound construction techniques and the provisions of the Party Wall etc Act 1996.  Loft Companies prefer working in timber, there being an apparent antipathy to bricks and mortar techniques.  To create a Loft Room the “modern” way to raise a party wall is in timber-framing.  If properly executed it is possible to design the raising of a party wall in compliance with the Building Regulations.  It is therefore difficult to argue against raising a party wall in timber unless it is reasonably foreseeable that an Adjoining Owner would be deprived of their right to do so, or incur additional costs in the exercise of that right.

To avoid serving notice under the Act some building designers opt to double up the rafters spanning parallel and adjacent to the party wall and support the dormer cheeks on timber framing, the external cladding projecting over half the width of the party wall.  Since the cladding does not bear on the party wall it cannot be described as the raising of the structure thus there is no requirement to serve a notice under Section 2 of the Act.  However, the disadvantages are that there is no legal right of entry onto the Adjoining Owner’s roof for the purposes of construction and also there is a risk that roofing battens, when cut for the works, may be left insufficiently fixed.  On the other side of the coin the Developer does not have to pay for expensive surveying services and the Adjoining Owner can, at a later day, raise the full width of the party wall in masonry or timber studwork.

An alternative to framing the dormer cheek is to raise the full width of the party wall as a double leaf of timber-framing incorporating the required sound, fire and thermal insulation, but this requires the express consent of the Adjoining Owner accepting the projection of the cladding over their side of the party wall, albeit the removal of the cladding to facilitate enclosure would be a simple process.

The “third” method involves serving a notice to raise the party wall in timber but in such a manner as to facilitate the Adjoining Owner replicating the work without incurring additional costs.  The advantage to the Building Owner of serving a notice to raise in this manner is the right of access under Section 8 of the Act.  Furthermore, it becomes possible to determine a long-term solution to detail the junction of dormers if and when the current Adjoining Owner carries out reciprocal development.

It is submitted that an acceptable method of construction, that is to say in compliance with Building Regulations and advantageous to the Adjoining Owner, is (viewed from the Building Owner’s side of the party wall), as follows: -

- An insulated plasterboard system cladding the existing party wall as well as the internal face of the timber-framed dormer cheek providing the necessary fire resistance, thermal and sound insulation and incorporating an integral vapour control layer all in the form of: - 
- Kiln-dried and regularised timber studwork of minimum finished section size 100mm x 50mm, ideally @ 400mm centres, but sized to suit the dormer construction, by a structural engineer or other suitably qualified designer.
- Non-combustible insulation, such as Rockwool, to fill the gap between the studs. 
- Structural grade plywood sheathing with a weather-resistant glue line of thickness to be determined by that necessary for the loadbearing parts of the dormer construction.
- 15mm thick calcium silicate board to achieve the required fire resistance for the overall system, as confirmed by appropriate available fire test data sheets.
- Breathable membrane.
- Vertical counterbattens fixed through the boarding/sheathing in line with the vertical studs behind to provide the necessary drainage and ventilation path behind the horizontal battens.
- Horizontal battens and tile/slate weathering.

It is, however, the Designer's responsibility to check with Building Control that the above specification is acceptable in their area.  The ultimate aim where both owners develop is to provide a timber framed party wall in compliance with the Building Regulations and initially without disadvantaging the Adjoining Owner. 

To provide the opportunity to form a long-term working detail where both owners have developed their dormers at the boundary, the head of the dormer cheek should ideally be constructed with an upstand above roof level, not less than 150mm high, which can be flashed over to form a weathering joint.  Where owners wish to join their dormer flat roofs the omission of this, or a similar, detail can and does lead to disputes.  It is appreciated, however, that to incorporate this detail in the dormer design may depend on the relationship between the height of the dormer and the ridge line.

This Article describes some of the common approaches to building dormers; however, many old terraced buildings were built without party walls in the roof attics, or the party walls are only half brick thick. In these circumstances some local authorities take the view that the raising of the party wall shall not be carried out to a lesser standard than used in the original wall construction, which implies the potential for serious inconvenience to the Adjoining Owner if steps are not taken to improve insulation.

In conclusion, provided an Adjoining Owner is not disadvantaged by the actions of the Building Owner, the raising of a party wall in timber framing in compliance with Building Regulations is acceptable.  

Keith Douglas FRICS. MCIArb

Phillip Cane MCIOB
Robert Moxon BSc. FRICS. C.Build E. FCABE. CMaPS
John Naish BSc. FRICS. MCIArb