Lead testing

[William Nohmor]

I bought a 3 family house in East Boston and am confused about lead testing and looking for some advice.

One unit is occupied and not renovated.

Two units have been renovated and everything is new.

Appropriate notices were given to the tenants about the renovation and lead safe renovation practices were used by a certified contractor.

My question is about lead testing.

The units have common stairwells and porches.  What is the sequencing for lead testing and who do I call to get it done?

The renovated units will most likely not have lead as they are all new walls, trim etc.  

The common stairwells may have lead.

The outside of the building may have lead.

So what do i test and 

when do i test? and

Who does the testing?

Thank you