3 Storey house extension
The original stone house is located in a semi-rural location, in an exposed location on the sloping site. There are several mature trees on the site. The detached house is small, built on a small footprint of only 40m2 (excluding the kitchen extension). The layout is a typical 2 up 2 down layout, similar to many terraced properties in the area.
The existing loft extension is considered an internal room and could not be used as a bedroom,. The staircase to the loft was built directly over the existing stair, again reducing the size of the principal bedroom significantly; stairs generally require a significant amount of space; resulting is smaller rooms.
The kitchen was located within a poorly constructed lean-to side extension. The original house was in need of updating.
The house is elevated on a hillside in an extremely exposed area; any work proposed would need to address this. The hillside location provides views to the North and West over the Pennines towards the Cheviots.
Client requirements and design
A new 3 storey extension replaces the kitchen extension (on the far side of the property (away from the busy road). The proposals provide a total of 4 Bedrooms; 3 larger doubles on the First Floor (including 2 family bathrooms) and a master bedroom with en-suite in the loft space.
The owners were looking to provide a feature space within the more public areas of property. As the design developed we discussed relocating the existing stairs to free up space in the original house. As work the new 3 storey extension was to be entirely new (with fewer restrictions) we agreed to create a feature staircase within a large full height stair void. Given the property faced due South onto the private drive it made sense to locate the full height void feature at the front. This design approach maximises potential solar gain in the winter (significantly offsetting heating costs on sunny days during the heating season. The rear (North) of the extension is dedicated bedroom space, with 3 of the 4 bedrooms and kitchen with uninterrupted views to the North. This early idea has driven the design, becoming is an integral part of the design.
Linking through to the existing property
It was a conscious decision to separate the old and the new, linking the two halves of the property via a series of modest doorways leading onto the new kitchen from the 2 original Living rooms. The clients wished to minimise disruptive demolition work to the main building. An opening on the First Floor landing links all bedrooms via the generous landing overlooking the drive to the South. On the top floor the new master bedroom has views in 3 directions and over the stair void below. The master bedroom utilises the original loft space (previously unused) as a dressing area and bathroom.
3-storey extensions: The potential problems extending a small house.
There is always compromise when extending any small house with a loft extension. as there is limited headroom in the loft space. This project was more complex still, as we were extending a 2 storey house with unusable loft extension with a 3-storey extension. Headroom was a key issue on this project, given the roof of the new extension could be no higher than the existing; a condition of the planning permission.
To make best use of available headroom, the Ground floor of the extension is set lower than the original house. This independence from the main structure allows a significant reduction in the height of the extension, incorporating a step down into the extension where it links with the original house on each of the floors. This was achieved by lowering the Ground Floor to below that of the existing house (site levels externally were reduced to avoid costly retaining structures and damp proofing). We worked closely with the engineer to minimise floor build-up. This solution allowed us to lower the top floor by over 500mm, significantly increasing the useable footprint of the top floor master Bedroom.
The entrance to the extension is across a small bridge accessed off the drive. the entrance lobby is on a half-landing, leading down 800mm to the Kitchen and up 1800 to the First Floor. The design is based on a request from the client to ‘terrace’ the landing spaces back into the house to create a light and airy void to the front of the property.
Detailed section demonstrating how stepping down into the extension provides a significantly larger loft room.
Services strategy: Solar heating and high thermal mass
The circulation and feature void spaces face due South with views onto adjacent fields. High level Velux rooflights provide additional natural daylight. They also allow for purge ventilation to avoid overheating of the atrium on sunny days. The extensive roof overhang over the glazing is designed to minimise overheating in the summer when the sun is strongest. The steel and masonry construction (with concrete Ground Floor) provide significant thermal mass to absorb excess heat during the day, re-emitting it as gentle warmth in at night when required.
The bedrooms are located to the rear (North) of the property, where thermal separation from the stairwell reduces the risk of overheating. A purpose-built high level duct draws warm air from the top of the void space into the back of the house to distribute warmer air to the cooler rooms to the North; this again reducing overheating on sunny days.
A key planning requirement was that any addition to the original building should be subservient to the original in scale and form. As part of the ongoing discussion the massing of the property was reduced. As the building progresses upwards there are a series of lean-to roofs as the floor plans reduce, creating a series of natural lean-to roofs that in turn break up the massing form and allow natural daylighting by way of Velux rooflights.
By superimposing the old massing model onto the new we were able to demonstrate a considerate reduction in scale, whist actually increasing the Ground Floor of the extension to provide a larger open plan kitchen on the Ground Floor, open to the stair void at the front. Stepping the building vertically both inside and out provided a sculptural quality to the property.
The size of original extension was reduced to meet planning requirements.
The design and conservation officer raised concerns about the original scale of the original design proposals. The model demonstrates the sizeable reduction in the scale of the proposals requested as part of ongoing planning discussions.. The revised extension is shown in blue, and superimposed onto the original 3d model..
Conservation officer response to design:
Thank you for the submission of 3D modelling….This has addressed the fundamental concerns raised originally as the height of the proposed extension has been reduced and the original forward projection replaced with a set back to the front building line which creates subordination from principle viewing points. The form draws some inspiration from the traditional domestic building type such as the rectangular base plan, use of steep roof pitches, and prominent gables, but places an emphasis on contemporary interpretation. The solid to void ratio has been increased with the glazing positions and styles revised so that the elevations appear less crowded which is appropriate.
The roof still remains subservient as requested by the planners, and the extensions still steps back on the North elevation to minimise its impact from the street.
Setting-out on site and construction.
The open plan nature of the extension over 2 stories gave rise to structural issues that needed to be addressed at construction stage. On site the Final Ground Floor level was established relative to the Ground Level of the existing house (it was only after demolition that we were able to measure the Floor level of the house and finally establish the floor levels for the extension.
A full height steel frame was required to support the roof over the full height void and to allow for the reduced floor build-ups (to maximise headroom and useable space). The steel frame required off-site manufacture, with the final steel sizes ordered from site dimensions as the design progressed. The entire extension design incorporated some significant tolerances (given the uncertain nature of works to existing buildings), with setting out meeting on site with the contractor to ensure the roof of the extension ran through with the original roof.