Sunday, February 22, 2009

The Design Brief

Having talked about the structure of the existing house at length, I suppose I ought to talk a little bit about what I would like to do with it during the renovation. My intention is to retain the period features where possible and to repair the existing structure as needed. As you might have guessed from the previous posts I will be replacing the UPVC windows, and possibly the front door (single glazed and badly fitted). Most of the existing roof will be getting replaced as well - although the front elevation will be similar to how it is now with the addition of some rooflights.

The layout on the ground floor (existing plans are shown above) is a result of the house being used for bedsits in the past and the old kitchen is currently the bathroom with a store/ WC sat in the middle. So the main aim here is to get the bathroom back upstairs where it belongs - giving more space to the living area. Of course this then means losing a bedroom on the 1st Floor. In order to keep the number of bedrooms and generally create more space we will be extending up into the roofspace (from the existing ridge backwards). The kitchen is also past its sell-by date so this will be replaced.

The result of the extension into the loft is that the hall stair will need to be enclosed and all the doors from habitable rooms (bedrooms and living room) onto the stair and landings will need to be of fire rated construction (FR30). This accounts for pretty much all the existing doors being replaced (none of them are original anyway). Another implication of this is that the plumbing will now have to extend up another 2 floors, so some duct space will be necessary and possibly a new boiler will be needed.

In the course of doing all this, most of the electrics will need upgrading/ replacing, and we will be taking the opportunity to add things like internet access and TV aerial points where needed. One bathroom will be stretched as the kids get older so an ensuite is planned for the new 2nd floor, and a cloakroom will be added on the ground floor. We will also try to add some sound insulation between the floors as we go.

Tuesday, February 17, 2009

What the Victorians Didn't Do for Us - Part 5


Originally, the windows would have been timber sash windows with the frames rebated into the brickwork. Like most Victorian joinery these would have been painted with a lead-based gloss paint - most likely white. The rebates (the inner opening is stepped back half a brick and the frame partly concealed by half a brick on the outside) help to protect the timber from weather exposure, and also hide the bulk of the boxed frame containing the pulleys and weights for the sashes. The openings have a stone sub-cill which casts water away from the window and the brickwork immediately around it - in this case these have been painted white. At the back of the house the openings are capped by brick arches in red brick. To the front there are stone arches above the windows treated similarly to the cills.

Sometime in the mid-80s the timber windows on our house were replaced by the previous owner with UPVC windows like the one in the picture above. Typically these have a maximum design life of around 20 years, and after that they begin to fail. In our case the ironmongery has started to fall off (handles are rivetted through the plastic and when these fail they can't be replaced), the glazing panel seals are deteriorating and some of the opening mechanisms have buckled (not particularly strong in high winds!). So one of the major tasks and expenses of doing the house up will be replacing all of these.

Interestingly these windows have much smaller frame sections than the originals would have had. So the original internal openings must have been boxed out for the new windows to sit properly in the external openings. Having tried fixing curtain rails etc internally I think that this has probably been done with plasterboard and newspaper! So another task once work begins is to determine exactly what has been done around the openings internally.

Of course replacement timber sash windows are expensive and are prone to the same problems that the original windows would have had leading to their replacement. In terms of the current regulations, the main issues are insulation, solar gain, ventilation and maintenance. The UPVC windows are awning casements (which tend to catch the wind!) and double-glazed. These days even this would not pass muster for Building Control, and better glazing, possibly with better frames would be necessary.

My own preference is to return to sash windows. Party this is on aesthetic grounds, but also because I think that ventilation is much better controlled with them than using trickle vents.
Getting a timber frame that will take double glazing means beefing up the frames for the extra depth, so these will always appear slightly bulkier than the Victorian originals which were single glazed with putty. The other alternative is to resort to UPVC or metal sashes or composite timber windows.

UPVC is still the cheapest option, but the sections are bulkier and it always looks like, well, plastic. Metal is problematic because it is a poor insulator. Composite timber windows are a good compromise, being virtually maintenance free, but more expensive than UPVC. These are timber windows with seals and thermal breaks which are clad in coated aluminium externally. If installed properly they have a long design life, and still give the feel of a timber window without the expense of repainting/ restaining every 2-3 years which a normal timber window would need. In my experience almost no-one bothers repainting until it is necessary (paint is falling off or the timber is rotting), by which stage the timber needs repairing as well.

While looking around at windows I did a quick count on our street. Out of roughly 100 houses nearby, about 90% had gone for the cheap UPVC option - in most cases doing away with sashes altogether. Within this there were virually no repeats, which reflects the number of manufacturers out there, I guess. They were also all uniformly plastic white. A couple had timber framed windows that were not sashes - these were probably installed in the 1950s, and about 2 had original sashes or very close reproductions of these. Strangely enough, when we moved here we looked at another property on the same street which had remained untouched since the 1930s. This one had the origial sashes, which were painted a dirty yellow/cream colour. These have now gone and the house has been renovated.

Anyway, getting back to our windows, my current thinking is to go with timber composite frames. These have a good thermal performance, negligable maintenance, can be made as sashes with glazing bars and house the latest thinking in double-glazing (special glasses with inert gas filling the cavity between panes). The other advantage that these have is that they are dimensionally stable - timber windows can warp and stick when their moisture content varies. This also helps with draft-proofing. The Scandinavians and Americans seem to have cornered the market in these, and 2 of the more well known companies are Marvin and Velfac. Of these Velfac doesn't do sashes, so if anyone knows of other manufacturers who do composite sashes drop me a line here.

Tuesday, February 10, 2009

What the Victorians Didn't Do for Us - Part 4

The Roof.

The pitched roof spans between the two brick party walls, and in this case is slate. The slates are overlapped so that at any point on the roof surface you get three slates thick. This is designed to stop leakage through the gaps (not entirely, but the law of averages means that during rain most of the water flows down the roof slope rather than through the gaps). The slates are nailed to timber battens, which in turn are supported on the roof rafters.

Unlike a modern roof, there are no trusses, and the structural frame is braced by the purlins and cross braces at centre span. In addition there is no roofing felt under the battens and over the rafters. In a modern house the felt stops drafts, and ensures that any water that gets through the slates has a path down the slope to the eaves. The Victorians didn't have an equivalent to this, and their buildings were built this way to ensure maximum ventilation to both the roofspace (to prevent the growth of wood rot) and also to allow air in to fuel the coal and wood-burning fireplaces.

You can see on the right that the rear chimney breast has been removed, and the remaining stack is now supported on a concrete lintol bearing on a steel L-section bracket. This is in accordance with the latest regulations, but it would have helped if the previous builder had cut the lintol back and had enough confidence in their work to remove the additional timber props under it! Perhaps refixing the purlin support would have been a good idea as well?

The battens and slates continue over the party walls and form a continuous slate roof between the adjacent properties. There are no firestops at this point, and the pointing on the party walls is intermittent, so there isn't much of a smoke barrier either, in the event of a fire next door. Where the roof abuts the chimney the rafters are trimmed, and the slates are cut and made weatherproof by using lead flashing. This is thin sheets of lead, tucked into the slate courses and bedded into the vertical surfaces of the brick chimney.

The chimney itself normally has a slate course at the top acting as a dpc to stop damp moving down the brickwork from the top. Similarly lead sheet is used as a valley gutter where the rear outrigger of the house hits the main roof. At this point it sits on what is known as a valley rafter (here this is just a couple of boards, rather than a full beam).

Friday, February 6, 2009


As I'm new to the blogging world, if you have any suggestions for the site, or think that the information or layout could be improved, please let me know.

Its beginning to dawn on me that this blog is going to need lots of diagrams and sketches (just like the real drawings!), since the web is not great at displaying large architectural layouts. I think that it may also need to be organised differently to allow people to drill into the information here as it builds up and find the links to other sites as I add them.

Right now I'm concentrating on documenting the house, so that people can gain a basic understanding of the existing structure and why things are the way they are. Some of these posts will change as I think of better desciptions or add better graphics. Later on, the plan is to discuss the implications of the current building's structure when trying to meet modern standards and regulations, and perhaps come up with some general solutions.

What the Victorians Didn't Do for Us - Part3

The brickwork of the house provides most of the load bearing structure and carries the weight of the floors and roof down to the footings. The image above shows a typical long cross-section through the house, mirroring the one from the 1898 drawings. Bricks are modular and sized so that they are twice as long as they are wide. In the 19th century there was less standardisation than there is now, and inevitably the bricks on our house are not standard. This poses problems if there is any damage to the bricks since any replacement is not necessarily the right size! Modern bricks are standardised at 215x102x65mm (9x4x3 inches approximately). The facade uses 3 or 4 types of standard brick: stock facing bricks for the main walls, slightly rougher ones where the walls are not exposed (such as in the loft on the party walls), red bricks for the brick arches over windows and decorative string coursing (single courses of brick which break up the pattern of the facade), and slightly redder bricks on the front bay.

The bricks are laid 9 inches thick for all the external walls and the party walls between the adjoining terrace. Load-bearing walls on the ground floor are a single half brick thick (4 inches). The coursing is what is called Flemish bond, and there are lots of special bricks which are used to turn corners and ensure that the coursing works. To find out more about bricks, Ibstock offer good technical advice here.

All the windows and doors have stone cills which have been painted white. The rear windows have flat red brick arches over them, and the front ones have stone ones (the structure is actually carried by the timber lintol behind these).

At ground level, where the bricks continue below the slate dpc, they are dressed with a cement render which further protects them from frost and damp.

Wednesday, February 4, 2009

What the Victorians Didn't Do for Us - Part2

I'll start at the bottom with the below floor stuff

Firstly, in this part of London the soil is clay and subject to a fair amount of movement and subsidence. If you look carefully at the photo of the front facade, you can see that the bay on the front is in a different brick to the rest of the walls and most likely has been rebuilt in the past.

The Victorians approached structure from the sole point of keeping things standing. Damp-proofing was rudimentary, and the brick structure was flexible enough to withstand most ground conditions. At that point in time they didn't have a knowledge of plastics so dpms (damp proof membranes or polythene to most people) did not exist. The brick external walls are solid and 9 inches thick. These are made of bricks that are quite soft by today's standards and would have been bedded in lime mortar (importantly this is roughly the same softness as the bricks- ie. it's slightly crumbly - these bricks still hurt if dropped on your head!). At the bottom the bricks step out to rest on the concrete strip foundations and this helps distribute the load since the footings were not reinforced.

They were aware that damp rose in the porous brickwork and that this could damage timber, so they built layers of slate 6 inches above the outside ground level into the brick walls. The slates were lapped and stop the water rising from the ground below. In addition to this, the void under the timber floor is ventilated to further reduce the moisture level in the bricks and timber. So all the external walls are punctured by air bricks below the level of the slate dpc (damp proof course - these days this is usually bitumen felt rather than slate). The timber floors are suspended above the ground on brick stub walls (built with holes in the coursing to allow air through). This means that the ground floor is supported independent of the potentially damp outer walls and ventilated from below. To stop moles and provide some stability to the party walls there is a ground slab laid between the concrete footings.

The important thing to realise is that if you compromise the ventilation the damp-proofing doesn't work and the chances are that your timber will start to rot. People tend to block the airbicks accidentally, or else deliberately to reduce the cold air drafts internally. The traditional airbricks are also great for letting in mice which is another excuse to block them. Repointing the brickwork with modern cement mortars can also cause the soft bricks to spall from frost damage and crack with movement.

Another issue with this type of suspended floor at ground level is: how do you insulate it? The stub walls are deliberately sited to reduce the depth of the joists needed to span under the floorboards. On this house this means that they are only 4 inches deep (even with the best insulants this will not meet the current Building Regs standard).

The next installment will talk a little more about the walls....

Monday, February 2, 2009

What the Victorians Didn't Do for Us - Part1

Well for starters, they didn't do a lot of drawings. These houses were their equivalent of building mass-production, and there are huge numbers of similar ones all over the country, with minor variations. As a result the Victorian architect could rely on his builders to interpret a very basic set of drawings (in this case 2 for the whole road). If I did this so economically today it's likely I'd be sacked or at the very least sued further down the line!

Below are the drawings that I dug out of the local council archives (Building Control had them on microfilm and printed them for a small charge):

I'll be returning to these later when I get round to talking about construction in Part 2.