Hi All,

I'm helping out with the re-plumbing of a house, the house has been gutted
and significantly extended. So rather than adding a new bathroom and just
joining the pipe work onto the existing pipes, I'm in the situation of
there's the domestic supply pipe we need a bathroom here and here etc.

My first question is really about the sizing of the pipe, the house in
question will have 3 bathrooms ( I've been told it has low mains pressure);

Up-stairs bathroom 1 bath, 1 w.c, 1 basin, 1 mixer shower.
Downstairs cloak room with 1 basin, 1 w.c
Downstairs shower room with 1 basin, 1 w.c, 1 mixer shower

The owner has been advised by the builder that a 15mm supply will be
adequate, now I'm no plumber but when you also include the sink, washing
machine and dish washer into the equation and not forgetting the supply to
the combi boiler. I don't think this is right, gut feeling is 22mm (boiler
has 22mm connection anyway) reducing down to 15mm at the furthest point
seems to be more sensible. Anyone any thoughts on this?

My second question is more straight forward. Because of the location of one
of the toilets, I need to lay a horizontal run of soil & waste pipe which
will have 2 toilets on it, what fall should the pipe have?

And lastly on the above soil & waste pipe, I believe its ok to use a
strap-on boss to join the basin waste to it as long as its not within 200mm
of the wc connection or does this only apply to vertical soil pipes?

Hope someone can shed some light on these questions.

Many thanks.

Jeff