How far from the house should ash and silver birch be planted

I'd say that was far too near. How big is the ash tree??

The rule of thumb is to look at the width of the canopy and the roots will stretch that far, as well. Ash trees are potentially very large trees - and the roots are likely to damage your foundations once it gets going! Not only that - the tree will make your rooms dark and the branches will swish against the windows, too!

The silver birch is probably far enough away not to concern you.

Sounds to close to me and your gutters will get very full too. Where are your underground services? The one with the roots in the lawn are you sure its a silver birch?

General advice re tree planting is no nearer than 40 feet to a building. The Ash needs to go a.s.a.p., the Birch, well, that's up to you - depends which one you've got, but none of them are particularly small trees, think the shortest is about 30 feet in height, with probably an equivalent root spread.

oh my goodness
this all sounds very scary
is it a new house for you? if so im suprised nothing was said by a surveyor

x x x

so Bamboo the enginer from Welsh water was only 18inches more than you LOL