Reinforcing 1st floor joists

[larry]

Hi all

In the process of renovating an upstairs bathroom and have pulled out a run of four poorly located 15mm pipes which were notched towards the middle of the joists (so approx a 60mm X 15mm notch). Span is approx 3.2m and the notches are approx 1.2m from one wall so certainly not right in the centre but most of them won't need to be used so feel I should make good whilst boards are up. 

 

From various forum based research I had planned on reinforcing with strips of ply both sides of the joist, glued and bolted, as long as I could get it along the span. Was planning to use 12mm thick strips, but on both sides. Helpfully however Wickes has sent me non structural Hardwood ply rather than structural softwood ply that I ordered. 

 

The picture shows 3 notches but in total the run is across about 7 joists. 

 

Question is, go ahead and use it what I've got, save it for another project (can't deal with the hassle of moaning to Wickes!) or use something else entirely? Thank you all! 

 

 

[PeterW]

Use the ply they have sent but TBH those notches aren’t bad. If you’ve got some timber offcuts you could also fill the gaps with even better. 
 

I wouldn’t bolt it either - plenty of decent D4 foaming glue and 5x50 screws will be fine. Those joists look ok - did the floor move before ..? And are you removing all the floorboards ..??

[TonyT]

Agree with PeterW.

 

I did just this 2 years ago on a few joists where my boiler was to be located.

i used 18mm ply, wood glue and spax screws.

its not moving.

 

seen plenty of houses with plumbers/electricians notches and this depth never caused any bother.

 

 

[tonyshouse]

+1 and No action needed, use the notches, don’t drill any holes near them 

[larry]

59 minutes ago, PeterW said:

Use the ply they have sent but TBH those notches aren’t bad. If you’ve got some timber offcuts you could also fill the gaps with even better. 
 

I wouldn’t bolt it either - plenty of decent D4 foaming glue and 5x50 screws will be fine. Those joists look ok - did the floor move before ..? And are you removing all the floorboards ..??

Thanks Peter. Reassuring. I've got some 2 X 4 CLS so could use that instead if likely a better solution?

 

Not any movement or springing. The ends are a bit cut up too in places (more notches, but smaller). Possible that we will put an unvented cylinder on the floor though -if not now at some point down the line-so keen to try and sort out.

 

Not all floorboards will be lifted, I have a new stud wall now running along in the direction of the floorboards. So suspect getting a full length anything down may be tricky.  

[larry]

Thanks everybody for such quick responses and helpful advice. This forum is brilliant. 

[joe90]

Frankly I would wallop some tight pieces of wood into those gaps with a bit of glue. Any bending of a floor joist compresses the top layer so if it’s filled (tightly) it ain’t going no where. I was always taught to drill holes in the middle of joists which compromises their strength the least. (Difficult to get copper pipe in tho, thank god fir plastic pipe!).

[larry]

13 minutes ago, joe90 said:

Frankly I would wallop some tight pieces of wood into those gaps with a bit of glue. Any bending of a floor joist compresses the top layer so if it’s filled (tightly) it ain’t going no where. I was always taught to drill holes in the middle of joists which compromises their strength the least. (Difficult to get copper pipe in tho, thank god fir plastic pipe!).

Indeed, agreed very much on the plastic pipe front!!

[Onoff]

34 minutes ago, joe90 said:

Frankly I would wallop some tight pieces of wood into those gaps with a bit of glue. Any bending of a floor joist compresses the top layer so if it’s filled (tightly) it ain’t going no where. I was always taught to drill holes in the middle of joists which compromises their strength the least. (Difficult to get copper pipe in tho, thank god fir plastic pipe!).

 

Same here with the bits of wood in tight & glued.

 

Isn't the current hole drilling zone between 0.25 & 0.4 of span? Various drawings about. Maybe in the OSG? Electricians Guide To The Bldg Regs? I'd get up and look but it means leaving the tin of Celebrations unattended.

[PeterW]

1 hour ago, larry said:

I've got some 2 X 4 CLS so could use that instead if likely a better solution?

Oddly enough, no... ply glued and screwed will strengthen that better than a couple of short bits of timber, but as @joe90 has also said, get those gaps blocked up too to keep it all in compression on the top chord. 
 

Are you putting ply over the top of the floorboards ..? 

[larry]

5 minutes ago, Onoff said:

 

Same here with the bits of wood in tight & glued.

 

Isn't the current hole drilling zone between 0.25 & 0.4 of span? Various drawings about. Maybe in the OSG? Electricians Guide To The Bldg Regs? I'd get up and look but it means leaving the tin of Celebrations unattended.

I think you are right, does this answer without risking the chocs? https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists. 

 

(Which means I guess my notches are currently outside what is now permitted, though holes instead of the notches would have been fine)

[larry]

1 minute ago, PeterW said:

Oddly enough, no... ply glued and screwed will strengthen that better than a couple of short bits of timber, but as @joe90 has also said, get those gaps blocked up too to keep it all in compression on the top chord. 
 

Are you putting ply over the top of the floorboards ..? 

Thanks Peter! 

Wavering over what to do with the top. Balance between not wanting to lift another board for the next ten years and knowing that almost certainly I'll want to!! But yes, a possibility. Guess that would help with load distribution?

[Onoff]

2 minutes ago, larry said:

I think you are right, does this answer without risking the chocs? https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists. 

 

(Which means I guess my notches are currently outside what is now permitted, though holes instead of the notches would have been fine)

 

Plenty of places where the holes are outside what's now considered proper. They're all still standing. 

[Gus Potter]

Hi Larry.

 

40 minutes ago, larry said:

Thanks Peter. Reassuring. I've got some 2 X 4 CLS so could use that instead if likely a better solution?

 

Not any movement or springing. The ends are a bit cut up too in places (more notches, but smaller). Possible that we will put an unvented cylinder on the floor though -if not now at some point down the line-so keen to try and sort out.

 

Not all floorboards will be lifted, I have a new stud wall now running along in the direction of the floorboards. So suspect getting a full length anything down may be tricky.  

 

Yes, it's a great place to pick up knowledge and get a bit of encouragement in the process.

 

If you want to add in something heavish later then it's worth while having a quick check to avoid any unwanted surprises later. It may be that you don't need to do anything at all.

 

For all too. I have copied a link to the LABC site which gives some general rules on notches in solid joists. There are plenty other places where you can find this info.  Much you see here is based on the BS and Eurocode standards but I have not copied direct from the standards in part due to copywrite.

 

The bit that is missing from much of the info you can find as a self builder etc is the definition of a notch! The depths, positions etc are laid out for you but how long can a notch be before it stops being a notch? For the really keen you can find info on this in the USA codes for example.

 

But as a guide the notch length is recommended to be no more than 1/3 of the joist depth. Larry, have a measure and see if you can just leave them as they are if you want. If you later put the cylinder near the ends of the joists it will often be the case that the shear force starts to dictate whether the joists will be ok, so long as the joists are notched not too close to the ends.

 

I chucked this bit in above for all as from time to time you'll get some "cowboy" cutting too long a notch and claiming it follows the rules!

 

Glue! It's great stuff. A lot of glues are "stronger" than the wood, the screws provide the "clamping" effect and for simple analysis you can just ignore them after that and rely on the glue.

One key here if is to just be careful on the selection of the glue. To do a technically correct repair you want to consider using a "structural glue". Have a look at D4 rated glues. The "D" refers to the durability and related more to "non structural" applications. An alternative, I have used, is Cascamite (a resin type glue) which comes in a powder.. messy but good stuff and it's a structural glue. You can just mix what you need as you go. Lastly..make sure you clean the surfaces well as if not you may as well use sellotape (exaggerating a bit for drama), or just put the flooring back down.

 

 

 

 

 

 

 

[larry]

A huge thank you for this very comprehensive post - a few comments/replies back below. 

 

 

1 hour ago, Gus Potter said:

 

Hi Larry.

 

 

but how long can a notch be before it stops being a notch? For the really keen you can find info on this in the USA codes for example.

 

This sounds more like a philosophical question. Is the next step up, after a notch, perchance professionally referred to as a botch?

 

 

1 hour ago, Gus Potter said:

But as a guide the notch length is recommended to be no more than 1/3 of the joist depth. Larry, have a measure and see if you can just leave them as they are if you want.

 

This is helpful. They are a little bit above a third. 

 

1 hour ago, Gus Potter said:

If you later put the cylinder near the ends of the joists it will often be the case that the shear force starts to dictate whether the joists will be ok, so long as the joists are notched not too close to the ends.

 

That's also helpful! So a little more detail might be helpful here then. The joists run between an RSJ and a wall, as I say the total span is about 3.2m. The cylinder if installed would be at the RSJ end, probably with its centre about 80cm from the wall. The joists at this end are  fairly unadulterated in terms of notches and holes (there are a few holes for cables, but not many). At the other end, however there are two additional notches for cables and pipes. One is about 100mm (carrying cables) and one about 40mm wide (pipes). They are both within approx 450mm of the wall. These look to be older notches than the ones in the photo above  and need to remain in situ to carry pipes/cables.  

 

1 hour ago, Gus Potter said:

I chucked this bit in above for all as from time to time you'll get some "cowboy" cutting too long a notch and claiming it follows the rules!

 

We bought our house from a builder who had done an impressively superficial job all round. We love the house and have absolutely no plans to move but there has been an awful lot of 'clawing back' generally and then working out how to put things right along the way. It's meant an awful lot of working out the difference between things that are just plain wrong from things that might be a bit lazy but not seriously problematic, to things that actually are OK. Given I'm not in the trade, though handy with most things and happy to learn, half the work is working out which falls into what category.... 

 

One small example  from the first category was a spur off a spur off a spur off a spur to a 25 metre run of 1.5mm T+E cable in the garden, buried 2 inches below the ground in no protective conduit, to a metal backbox, fitted to a metal shed, with condensation dripping down the inside of the shed roof and into the back of the backbox, to then another spur, again in another 10m unprotected run, to another shed... I realised something was wrong when my 400w jigsaw led to the shed light dimming.... 

 

We've found several horrors however, which has led me to be very mistrustful basically of everything we find in the house that's had the previous owner's hands on it (the signature mark being 1 inch plasterboard screws used for absolutely any and every purpose). 

 

1 hour ago, Gus Potter said:

Glue! It's great stuff. A lot of glues are "stronger" than the wood, the screws provide the "clamping" effect and for simple analysis you can just ignore them after that and rely on the glue.

One key here if is to just be careful on the selection of the glue. To do a technically correct repair you want to consider using a "structural glue". Have a look at D4 rated glues. The "D" refers to the durability and related more to "non structural" applications. An alternative, I have used, is Cascamite (a resin type glue) which comes in a powder.. messy but good stuff and it's a structural glue. You can just mix what you need as you go. Lastly..make sure you clean the surfaces well as if not you may as well use sellotape (exaggerating a bit for drama), or just put the flooring back down.

 

This - also incredibly helpful. My geography means I'm limited to Homebase, Screwfix and a very handy Ironmongers. I might see what they stock. Alternatively of course there's the interweb. I'll definitely avoid the cellotape & good point about keeping the surfaces clean. 

 

 

[larry]

An update from today, following all the helpful advice last night.

 

Went to Ironmongers and bought D4 foaming glue (wow, amazing stuff) which seemed the best they had.

Cut the ply into strips.

Realised, of course, that the floor/ceiling has a Heringbone down the middle, which I'd forgotten was there (despite having looked at the many photos I'd taken of the underside when we had the ceiling down recently). That limited my total possible span of the ply to about 1.5m which I decided was still worthwhile even if not ideal. Who knows.

Cut the ply strips down to size!

Put glue, clamps and screws in.

Filled the middles of the notches with offcuts as suggested, and plenty of glue. Weighed down with a brick to counteract the expansion of the glue (of course the brick the stuck to the top!)

. Generally happy with efforts. Most joists looked fine except one which had a crackl on one side - nothing obvious I could see to cause it. Hopefully the ply/glue will help that also. 

 

Thanks to all for their guidance. Might need to start a post about some rotten rafter ends... was waiting for the carpenter to have a look but given how helpful you all are....