Infill urban houses

Part 2 - Construction.

Last year DHV Architects completed a small new build, detached mews house in a backstreet in Cotham in Bristol. The plot was formed by subdividing the garden of a large victorian villa. This is one of several infill developments we have designed over the past ten years. Although each infill housing project is uniquely designed, they share recurring challenges that must be carefully addressed throughout the construction stage.

1. Party walls

The plot is sandwiched between thee other properties, each with multiple owners. Party Wall notices had to be served to all adjoining neighbours for a total of nine separate Notices involving two different party wall surveyors. It took eight months for all the Part Wall Awards to be finalised, which delayed the project's start date by several weeks.

The site during construction

2. Retention structures.

Building partly underground requires a retention structure to protect the external walls from the pressure of the surrounding soil. In this project a thick, reinforced concrete wall was built on three sides of the plot. This concrete wall formed the outer leaf of the cavity wall, thus combining two functions in one structure. Nevertheless it was a very expensive piece of construction, and it meant that a considerable chunk of the budget was spent even before getting out of the ground.

The beam and block flooring and retention walls

3. Tanking.

Any structure built below external ground level needs to be protected from moisture ingress. There are different tanking methods, either a cement-based coating which is applied to walls and floors, or studded plastic membranes which are fixed to the outer walls (internally or externally, depending on the type) to create a waterproof barrier. In order to issue a warranty, tanking companies will normally insist on a double layer of tanking.

4. Rainwater sewer connection

In Bristol’s historic neighbourhoods (as in many UK cities), the existing drainage network is combined, meaning that rainwater and wastewater are discharged into the same sewers. During heavy storms, these systems can become overloaded and overflow into rivers and other watercourses. To address this, water authorities now restrict the amount of rainwater that can be discharged into combined sewers. Where stormwater cannot be managed through rain gardens or soakaways, it is sometimes possible to install a sealed attenuation tank. This system stores rainwater temporarily and releases it at a controlled rate into the combined sewer via a flow control device.

For this project, the external courtyard is fully lined with sealed attenuation crates, which fill during storm events and gradually discharge the stored rainwater at a controlled rate.

The attenuation crates

5. Photographic evidence

Since 2022 the construction of new dwellings needs to be documented in photographic form to prove that the actual build matches the details as drawn. The aim is to ensure airtightness and continuity of insulation across the key building junctions (floor/wall, wall/windows, wall/roof etc.). The photos, geo-tagged and dated, are submitted to Building Control before the completion certificate is issued.

6. Airtightness testing

Before completion of the building work all new build homes need to pass an air tightness test. A blower door is fitted in the front door, and a powerful fan creates a pressure difference inside the house, forcing air to escape though cracks and gaps. The rate of leakage as measured should match the parameters established at design stage. If not, remedial work is carried out and the house is re-tested.

7. Water efficiency

Increasing water consumption is putting pressure on the water supply and water efficiency is now a key requirement of the Building Regulations. All new homes need to limit their water consumption to 125 litres/day per person, which is achieved through low flow shower heads, aerated taps, low flush wcs and small baths.

8. New build warranties

New home warranties (also called 'structural warranties') protect buyers from defects arising within the first ten years after completion. Because most lenders require new build houses to be covered by structural warranties to qualify for a mortgage, developers need to plan for this at the start. Warranty providers will carry out a compliance check of all technical drawings, calculations and specification before the project starts on site, and then will inspect the work at regular intervals throughout the build.

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You can see more photos here. https://www.dhva.co.uk/new-build-house-cotham-bristol

Conclusion

Designing, planning and building a new home is a complex task which involves specialist knowledge - ranging from design flair to local planning knowledge and detailed technical capabilities. DHV Architects have the skills and experience to guide our clients through every stage of the process and create beautiful spaces tailored to their needs. Contact us for a no obligation discussion about your project on 0117 914 8317 or email info@dhva.co.uk.