We're in the process of renovating one of our ground floor rooms and when we
removed the ceiling we discovered one of the joists in the floor above has
been heavily damaged over the years by woodworm (which has been recently
treated). I can wiggle the joist around and it has the consistency of cork.
Two other joists are also damaged but still seem to have strength. My first
plan was to remove the damaged joist and install a new one but I've realised
this is going to be difficult since one end is imbedded into the exterior
wall and the other end imbedded into the sleeper (is that what it's called?)
running across the fireplace hearth. Would my best bet be to run new joists
in parallel with the existing ones using joist hangers? I've not used joist
hangers before, is there a write-up somewhere on the Internet on how to use
them? Thanks for any help. The link below is to some pictures of the
Woodworm attacks start in your loft, fact. If it is Woodworm, you'll know
if you see the little burrow holes, the only remedy is to replace the whole
thing after you've treated the whole area with an appropriate solution to
rid you of the problem. Woodworm don't just sit in the wood, but do, in
adult form, sit inside the cavities of the brickwork and other little hidey
holes, and only when they mate and lay their young on the soft wood, do they
show up as burrowing little maggots. It's not the adult woodworm that
causes the problem, it's the young maggot that destroys the wood.
Have it checked out properly by Rentokil or some such company.
If it is only rot caused by dampness or fungi, then take the road of
replacing the whole of the effected area with a damp proofing timber
preserver, and make good any parts that have or are going to eventually fall
off. Do it properly now before you end up with another load of work to do
in a few months time.
Thanks for the replies. In fact the 1st floor has only just been treated by
Rentokil. I called them in as soon as we saw a problem under the
floorboards. I asked their surveyor to assess the structural integrity of
the floor and he said it seemed to be ok but suggested we install supporting
timbers (for the floorboards) along the joists where the damage is the
worst. I thought about delaying the treatment until we had removed the
ceiling underneath but decided to go ahead as otherwise it would have meant
delaying the renovations. It's only now that we've removed the ceiling that
we can see that the one joist has suffered quite badly. There doesn't
appear any sign of rot, the damage does seem to be purely insect
infestation. I have a section of the joist which has been cut out by a
plumber and it is totally riddled with tiny passages where the worms have
burrowed. The room has never been centrally heated and I wonder if this
hasn't helped (this is a 130 year old house).
Since the joists have been treated do you think I can leave them in place
and install new ones alongside? Or would cutting it out be better?
I'd really advise going for all new timbers where needed, and make sure the
surrounding masonry and window frames are well treated with insecticide and
preservers. An attack of these little blighters can be the death of these
old properties due to the timbers being dry and mature for them to live on.
It is a bit more expensive to complete, but once it is complete it gives the
peace of mind to know that it's all done right.
Good luck on it.
As suggested elsewhere, you need to confirm that the only problem is
woodworm, not some form of rot which may have spread into other parts of the
house; use a specialist firm for this.
Also confirm that the other damaged joists are still suitable - 'seem to
have strength' may not be enough of a test as they will be braced by the
floorboards above which are nailed into them.
Joist hangers are pretty easy - obvious when you look at them.
You should be able to replace your joists with new joists in the same
position if you use joist hangers.
You need the kind which fit flat to the wall/beam and are secured by
rawlbolts or similar.
The more common type has a hook at the top to fit over a cross beam or into
a brick/block wall and is (I think) intended more for use when you are
building a new structure..
Couldn't find an Internet site with instructions with Google, but didn't try
As a rough guide - and with no warranty attached:
Supporting the floor via props under other joists (for belt and braces) then
remove the dodgy joist.
You will then have to fill in the hole in the wall with brick.
Depending on how the other end is fixed to the fireplace you may have to
fill a hole there as well; on the other hand it may just be skew nailed to
the cross beam.
Prop your new joist into place, then secure with a joist hanger at either
end, bolted to the wood or brick.
AFAIK you secure the joist to the joist hanger with nails - at least there
are loads of nail shaped holes in the sides of the hangers :-) Before you do
this you may need to knock small wedges between the bottom of the hanger and
the end of the joist to ensure the joist is tight up against the floorboards
Oh, and you will have to remove and replace the nails which are through the
floorboards into the joist - this may be all that is holding the old joist
This assumes you have confirmed the type of infection and treated
surrounding areas and the replacement joist accordingly.
You main challenge may be to find a joist and hangers to match the size of
your existing joists.
There is no reason why you can't put a joist either side of the damaged one
instead of replacing it directly - putting just one joist in alongside the
old joist might weaken your floor as it would give you:
Joist<small gap>New Joist<Large gap>Joist
Ignoring the shaky breaky part you are replacing.
One problem I see from the pictures is that you have cables running through
your joists somewhere near the middle.
Without re-running your cables you are going to have to find enough slack to
lift the cables up into a notch on your new joist(s).
However there does look to be a reasonable amount of slack (but check before
If you have to replace more than one joist then this can become a problem.
One other thought - if the joist is damaged in the middle only it is
possible to replace part of the joist by joining in a new piece and
reinforcing the joins.
I would recommend the purchase of a good DIY book (e.g. Collins or Readers
Digest) after first checking that it gives you the information required. The
cost is not much compare with the cost of getting this wrong, or employing
someone to do this for you.
As stated before, there is no warranty with these suggestions - they may be
totally wrong so you take your chances!
Thanks for the detailed reply. I've just replied to one of the other
replies about the woodworm/rot, I can't see any signs of rot and the wood
does just seem to be riddled with tiny passages/holes (but I'm no expert on
rots...) I think what I'll do is take up the floorboards upstairs and then
decide whether to remove the old joist or not. I'm rather hoping I can
leave it in place and run new ones on each side with joist hangers. In fact
I'm thinking of running 3 joists as this would help support one of the other
joists which seems ok, but may not be. Anyway thanks, you've given me
confidence that using joist hangers may not be that difficult, I'll visit a
bookshop and a browse a copy of Collins :-) I may also be lucky with the
cables as there is a loop at each end before they disappear into the wall,
there might be enough slack...
I think you are about right except in a couple of places:
I believe there are two main types of hangers. One for use during
building. The bricklayer puts them in instead of leaving an hole for
the joists. The other is more general. You nail them over the
"trimmer" or joist to which you will be butting up to.
This one is a new one on me. (I spy a trip to a timber yard before
Use zinc treated clouts and do not use wedges rather choose a size of
hanger that is a little smaller than the joist so you have to notch
out an housing. This will allow you to put the plasterboard flush.
Plenty of dust sheets and a filter-mask if there is any poison in the
And now the biggie:
Why didn't Rentokil replace the joists? It's unusual for them to miss
a section and the guarantee should cover it all, surely?
This bit of advice was from long and bitter experience of trying to fit such
things so that they hold something else tight (if you get my drift).
What I expect to happen is that everything is offered up and the joist
hangers are bolted tight then there is just a little play (millimetre or so)
when the props are taken away. This can be taken up by putting fillers
between the joist and the hanger (wedges was the wrong term) to take up any
flex in the hangers and get the joist really tight against the floor above.
However if the OP is going to take up the floorboards then this problem may
go away - althoug I suspect to get the joists perfectly flat across the tops
you may have to pad between the joist and at least one hanger. [Or I may
just be cack handed and a victim of Sod's Law].
Which leads me to wonder how level joists are in new buildings, and in old
buildings which have settled over the years....
Thanks for all the replies, I'll answer to all the posts here rather than
reply to each individually
I'm going to take Bigwallop's advise and remove the old joist and replace it
with new. My only concern about this is that it looks like it might be
tricky to get a joist exactly the same size (the existing ones are 2.5" x
6.25"ish), so I'm considering installing two 2" joists to replace the old
one i.e repair the holes left and install one each side of the original
position. I quite like this idea as I can run further joists if required
between other joists in the floor if I think they need reinforcing.
Regarding joist hangers, I'm not sure how I could angle the joists into the
hangers if the boards are still in place upstairs, it seems easier to remove
the boards (the room is empty, there's no carpet of anything) and then drop
the joists in from above. I can then take my time chiselling out the corners
to get the joist(s) level with the others.
A couple of things I'm not clear about - when installing the hangers into a
brick wall, do they have to be bolted? Or is it sufficient to cut a small
chase into the wall, slot the hanger in place and apply some mortar? The
other ends of the joists have to be fitted to hangers that are fitted to the
joist running across the fireplace, I presume I need to find some sort of
hooked hanger that will hook over the joist. I had a look in a timber yard
over the weekend and they had some that had long ends which can be bent over
but they didn't look that strong. Are there stronger ones available or is
there a better way of doing this?
The question about Rentokil and why they didn't see this problem, I can only
guess about this but I think that the true extent of the damage was only
visible once the ceiling downstairs was removed. I'm pretty content with the
job they did, at least they didn't try to pull the wool over my eyes by
telling me the whole house needed excessive treatment...
The joist hanger provides support for the end of the beam against downwards
This is either done by hooking over a beam or wall, where the hook carries
the weight, or by directly fixing to a wall if the wall is already built.
Where you are directly fixing to the wall the fixings carry the weight, not
the hook (as there is no hook!).
So you have to think about how strong a fixing you need to carry the weight
of e.g. a 2" * 6" beam and the floor above (plus furniture etc.).
The ones I have used have large holes in them to take wall bolts - these can
carry a large weight.
If you are using these there is no need to chase into the wall; they are
designed to fix directly to the wall like a very large shelf bracket.
Page 141 of the Collins DIY manual has a picture of a face fixing joist
hanger but the usual sheds and B&PM don't seem to carry them - I had to go
to a specialist supplier on an industrial estate.
If you are taking up the floor you can then hook over the wooden joist by
In this case IIRC you just have to secure the hanger to the wood with nails.
The nails don't take the weight, just make sure the hanger doesn't shift or
This way you can be sure that the load is being taken by the hook at the
When I first saw these I thought they were too flimsy to take the load, but
apparently they work.
I guess you could cut a notch in the mortar above a brick and insert the
hook bit at the top of a hanger to take the weight of the joist.
However I am not sure if you are supposed to fix down through the top flange
into the underlying brick/block work.
The pictures on P182 of the Collins manual clearly show holes in the top
flange and presumably they are there for a reason :-)
However this may just be for nailing if you are fixing to wood.
P188 of the Collins manual has a good write up on replacing a joist.
Might be worth going into a bookshop and reviewing these bits.
P.S. with face fixing hangers you shouldn't have to take up the floor - you
prop the beam up, offer up the hangers from underneath the beam, bolt them
to the walls and Robert is your parent's brother.
However this method does not guarantee a tight fit up against the floor,
hence my comments about an extra spacer (packing) between the joist and the
bottom of the joist hanger to take up any slack. A piece of thin ply can be
looking at the photos the interesting bit is going to be dealing with the
wiring. Obviously, you can't simply drill a hole through the joists and
thread the wires through, so I suppose that leaves you with the only option
of notching the joists.
remember to have a google search thru this group for notched joists if
you're planning to do that - I remember there being a couple of discussions
about it in the past - the positioning of and depth of allowable notches
when it comes to maintaining the strength of the joists vs safety of the
email me at
richard at olifant d-ot co do-t uk
A joint reply to all the previous posts:
Thanks Dave for the info, and thanks Bigwallop/Alan for the links to hanger
suppliers - very interesting as they show usage and loadings. We're going
hanger shopping and ordering joists in the next couple of days. We've
already cut through the old one and it's ready to be removed. The others
seem to be ok but we're going to install new ones between them anyway.
I visited my local Waterstones 'library' and had a look at the Collins book
which is a great help. I do have one of these but it's 15 years old and
doesn't cover this subject too well.
Regarding the cables, there's 5 in total. 2 are lighting to the pendant
which are loose and can be fed through new holes. 2 are ring main which I'm
going to cut and feed through new holes then join with junction boxes, that
way I can avoid notching the joists and risk potential nail damage. The
other is co-ax aerial which I'll probably slot into a small 1cm notches
(fortunately it has plenty of slack).
I'll try to remember to take some pictures before we board the ceiling -
I'll post a follow-up.
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