Advanced Structural
Designs ACN 097 789 87
92 Vasey Cres Email mal@structuraldesigns.com.au
How can I tell if I can remove an internal wall in my house?
Following are the possible structural purposes
for an internal wall.
- The wall is holding up some
roof structure.
- The wall is holding up some
ceiling structure.
- The wall is providing lateral
resistance to wind loads (ie contains wind
bracing).
- In rare instances where the
roof slope is steep the wall may be hiding a tie beam, which enables the
rafters to prop a ridge beam.
If you go
into the roof space of a pitched roof house and can see that all of the
structure around the wall is constructed of fabricated roof trusses 1,2 and 4 are less likely to be a problem as the trusses are
likely to span from one external wall to the other. In some instances however where the house
takes on an L shape internal walls lining up with the external walls will be
load bearing. If there is any doubt at all ask as it is quite surprising how often
experienced tradespeople get this wrong.
In
instances where the walls clearly do not carry any vertical loads but carry
wall bracing we would normally look at an area where
wall bracing can be relocated if necessary and go ahead with the
demolition. We can also do a quick check
for metal strap wall bracing with a cover meter if options are limited. Even if there is no bracing in the wall it is
permissible to use gyprock clad walls to provide up
to 50% of the bracing in domestic construction so it is useful to have a
structural engineer check out whether its removal is pemissible.
If you have
a “cut” roof (no fabricated trusses) where the roof or ceiling is supported
from an internal wall it is often possible to move the support away from the
wall you wish to remove by adding beams in the roof space or turning existing
rafters into trusses. Do not make the
mistake of assuming the ceiling is not supported by the wall just because the
ceiling joists are continuous over the wall.
You should check span charts if there is any doubt!
If you have
a flat roof with exposed rafters and the rafters are running across the wall in
question, you may have one of two problems.
The first problem is that the wall may support the rafters and be
required to reduce the span of the rafters, which can be quickly checked. The second problem is that the rafters may be
broken at the wall, which can present more design challenges. In the second
case the rafter is not only supported by the wall but is either cut from above
to make it sit down on the wall (because it was bent on the day it was
installed) or alternatively two separate beams sit beside each other on the
wall. This last situation limits the
support options if you are hoping to keep the exposed rafters but solutions do
exist.
Unfortunately
no two projects are quite the same so you will require someone to climb up into
your roof to assess the situation. It is
often the case that when loads are relocated, walls may also require local
strengthening which may necessitate removing some wall sheeting.
It is
important not to extend the principle of trusses spaning to outer walls to
larger buildings as large trusses regularly use internal walls for support once
the span is over say 12 metres. If the
wall is directly under web members on a long span truss we suggest you check
the existing structural drawings before removing the wall. The same is also true for parallel chorded
trusses which will often only be spanning 6 to 8 metres. Unfortunately we are too often called out to
look at disasters where the builder has made assumptions that did not turn out
to be correct.
If you require
any more specific advice from an experienced structural engineer in Canberra
ACT or the surrounding region call Mal Wilson from Advanced Structural Designs
on (02) 61612171.