Back in early 2010, I was approached by a client who owned a sub-basement in Edinburgh's New Town. For those of you who aren't familiar, a sub-basement is one level under the regular basement! The floor level of the property was five meters below the street but because much of the New Town is built on a slope, the ground is higher on one side and lower on the other, so the rear of the property opened directly onto a communal garden.
The property was large.
Over 80 square meters and had several rooms, including a kitchen, utility, bathroom, living room and two large box-rooms. However, the Building Standards require a habitable room to have windows which provides both daylight and ventilation. The standards set a minimum size for these two requirements as a ratio of the rooms size, the bigger the room, the bigger the window.
If you are curious, the ratios are 1/15th for daylight and 1/30th for ventilation. So a room of 15 square meters (a reasonable double-bed room) must have a window with at least one square meter of glazing and at least half a square meter of that window must be openable to allow ventilation. This only applies to what the Building Standards call 'Apartments', "a room in a dwelling not used solely as a kitchen, store or utility room"
Under the regulations, the client's flat had only one Apartment, its living room, which had a patio door opening onto the communal garden at the rear of the property. The two large box-rooms on the street size of the flat had only one tiny window each, with about about as much glass as a microwave door and neither was openable to allow ventilation. Here were two potential bedrooms but, legally, they couldn't be used as such.
The client commissioned me to resolve this.
Following a Feasibility Study, we decided to excavate two external alcoves outside the existing tiny windows. We could then install openable glazing of the correct size into each alcove and the box-rooms could be classified as bedrooms.
You can see from the cross section below, that this excavation was not straight forward. The proposed external alcove is highlighted in yellow.
Two Big Problems.
For starters, the title deeds describe my clients land extending as far as the street but the surface of the ground was owned by the upstairs neighbour. We were able to secure the neighbours consent for the work, without which it might have been possible to get all the necessary approvals but we could never have built the alcoves without access over their property.
Secondly, there were structural concerns, to avoid accidentally demolishing five stories of 200 year old, Grade A Listed, World Heritage site, we decided not to widen the existing window openings. Known as cutting down a window, this is a trick of the trade that saves money, as well as structural gymnastics, by keeping the existing window lintel in place. The next problem was ensuring the new alcove didn't collapse under the weight of the surrounding ground. Finally, where would the rainwater go? We had to connect the alcove to the drainage system, otherwise it would flood!
The construction drawing below shows the level of detail required to make all of this possible.
Before any of this could be built however, there was the small matter of successfully applying for Planning and Listed Building consent.
Dealing With Planners
During this process, details of the type of new sandstone were agreed. Because the original quarry from which the New Town was built has long since closed, a close substitute had to be found. Eventually it was agreed to use Peakmoor sandstone, from Derbyshire. We also had to get samples of the type of metal work we intended to specify and have this approved as well.
Curiously, there is no specific regulation for the type of metal grill that should be specified in this situation. I imagine walking over this in stilettos would be challenging but we consulted with the neighbour and got her approval before installing it.
When Planning and Listed building consent had been granted, we prepared and lodged a Building Warrant application. We worked with McColl Associates, Structural Engineer, who have experience in this type of project, to design the technical details.
The client was keen to have the project built by a competent building contractor but also wanted the construction cost not to exceed the anticipated increase in the value of the property. This is an almost impossible request to consider and it was only because the site was in such a prestigious location that it was possible to do so. Had property prices been lower, then the cost of construction would almost certainly been greater than the increase in value.
I organised a competitive tender process.
Asking five contractors to participate, with the outcome being judged on a mixture of references and price. Eventually S. Ewing and Sons won the contract.
Work took three months to complete and was only delayed for one week, due to the discovery of a larger than expected manhole direly next to one of the alcoves.
The alcoves were dug one at a time and safe access was provided to the upstairs neighbour at all times. All the digging was done by hand, as there wasn't enough room for machinery. The stone blocks of the external wall were much larger below ground level than was anticipated and required serious effort by the contractor to cut down.
During construction we discovered the drainage ran in the opposite direction than was originally thought but a solution as found to allow the alcoves to drain rainwater efficiently.
This project was also one of the first in Edinburgh to benefit from the new guidelines on double glazing in historic Listed Buildings. We were allowed to install Slim-Line double glazed, timber frame windows, where the glazing is only 6mm apart and resembles traditional single glazing.
This project, although modest, was one of the most technically challenging I have yet taken on and the result is good. The project was delivered within the time-scale and budget envisaged and the client is delighted. If anything is shows the value of consulting with an Architect before considering such a project.