Basement escape well construction

[Mark Bennett]

In my new house we're proposing to have a basement. The plan is for the basement walls to be constructed from block/precast concrete, tanked on the outside and then insulated with a thick layer of EPS insulation. The basement slab will be laid on top of a layer of insulation, with slab and wall insulation meeting up around the outside. So far, so good - good performance, no thermal bridges etc.

However, for safety purposes we need to have an emergency escape route that doesn't involve the normal stairs, which basically means an escape well. See (hopefully) attached diagram for a plan view.

The question is how best to construct this to minimise thermal bridges between the main wall structure and the exit well, stop ground water filling up the exit well and maintain the tanking around the walls of the main structure.

I've looked in the PassivHaus details book, but there isn't really anything similar. or that is obviously easily adaptable.

Any ideas or thoughts are very welcome.

[Nick Grant]

Hi Mark

Usual detail in Germany is to make the stairs bit outside the thermal envelope with exterior door at the bottom and an Aco type drain between the two draining to fresh air.

I hope you are on a sloping or very free draining site!!

Nick

[Mark Bennett]

Hi Mark

Usual detail in Germany is to make the stairs bit outside the thermal envelope with exterior door at the bottom and an Aco type drain between the two draining to fresh air.

Thanks - this seems to be the best option.

I hope you are on a sloping or very free draining site!!

Nick

Unfortunately not on a slope, but should be reasonably free draining although we are likely to get hit by running water coming down a nearby hill and along the top of limestone sheets starting about 1.5m down. Hopefully we can find a solution for this, but I think we may need the backup of a sump pump in the exit well.

[Y Claire Jenkins]

Do all basements need a separate exit? The design I'm playing with at the moment has a half flight of stairs up to the main entrance hall, but this is also the stairwell going up to the rest of the house, so I suppose a fire could spread down and block the way out. Would an escape window be acceptable? I hadn't planned an external window in, and was thinking about a big glass panel in the floor above at one end and light coming down the stairwell at the other.
Thanks
Claire

[Mark Bennett]

Do all basements need a separate exit? The design I'm playing with at the moment has a half flight of stairs up to the main entrance hall, but this is also the stairwell going up to the rest of the house, so I suppose a fire could spread down and block the way out. Would an escape window be acceptable? I hadn't planned an external window in, and was thinking about a big glass panel in the floor above at one end and light coming down the stairwell at the other.
Thanks
Claire

Generally, yes but it is subjective to risk assessments and opinion. Each habitable room (don't get me started on that) must have two independent routes of escape "at all material times". Exceptions exist for bathrooms, dressing rooms, laundry/utility rooms and kitchens, i.e. anywhere that the usage model means it is unlikely anyone will sleep there.

Also, while not within the building regs as far as I can see, the guidance I have received states that you must not travel through another room to get to the escape.  This means that if you have two habitable rooms in the basement you will probably need two escape routes etc. (In fact, this seems to be contradicted in the Approved Document, but it's probably too late for us to make use of this.)

See: http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADB1_2006.pdf
Section 2.

Depending on the layout, an escape window (of a reasonable size) is likely to be acceptable.

You my be able to avoid some of this through the use of protected stairwells etc. depending on the design of the building, but this is unlikely in practice. You should discuss this with your building control office if (s)he is of the helpful variety.

[Y Claire Jenkins]

Thanks very much, Mark. It sounds as if we might get away without it, as we definitely wouldn't be setting it up to be a sleeping area, just utility, laundry, storage, maybe workshop type functions. Though they could perhaps argue that later occupants could change that, I think it would be unlikely with so little daylight.
We'll have to discuss with building control if we decide to go ahead with the basement.
Claire

[Mark Bennett]

Thanks very much, Mark. It sounds as if we might get away without it, as we definitely wouldn't be setting it up to be a sleeping area, just utility, laundry, storage, maybe workshop type functions. Though they could perhaps argue that later occupants could change that, I think it would be unlikely with so little daylight.
We'll have to discuss with building control if we decide to go ahead with the basement.
Claire

I'd recommend discussing it with building control relatively early. If they insist on a separate escape then it could have a big impact on the design.

[Y Claire Jenkins]

Mark
We'll definitely consult in good time, though we've still got three and a half years till estimated time to start building! There are still some major design questions undecided; I'm waiting for my copy of PHPP to arrive to try my hand at playing around with the options. The basement would be rather a luxury and probably make the house a bit larger than we had originally intended, as well as being costly. It would help get the figures into PH range, but we're not dead set on certification anyway.
What are the main advantages of the basement for your design?
Claire

[Mark Bennett]

Mark
We'll definitely consult in good time, though we've still got three and a half years till estimated time to start building! There are still some major design questions undecided; I'm waiting for my copy of PHPP to arrive to try my hand at playing around with the options. The basement would be rather a luxury and probably make the house a bit larger than we had originally intended, as well as being costly. It would help get the figures into PH range, but we're not dead set on certification anyway.
What are the main advantages of the basement for your design?
Claire

The main advantage is to increase the living space on a restricted plot. As a minor point distributing the living space across three stories helps to make our building close to a cube, which helps to minimise the energy losses per unit of habitable floor space. Compared to an equivalent floor space on any other number of floors it will be more efficient.

However, it's not without its problems - retaining walls/piling to protect neighbour's houses, waterproofing, cost etc. If the plot would support it we would be better off doing it all above ground, even if only on two floors, but this isn't the case.

[Y Claire Jenkins]

Thanks, Mark
It sounds as if your reasons for going along the basement route are much more decisive than ours.
We'll go on weighing it in the balance.
Claire