How to fill the gaps in party wall up to the rafters.

rudigarude

Hi Everyone (hope you are all well),

Bought our house (semi 1930's ex-LA) house about 18 months ago and I am continuing to fix various issues. One that cropped up on our Building Survey was gaps between the rafters and the party wall, highlighted understandably as a fire hazard. I'm wondering what the best way to fill this would be.


Would something like this work okay (fire rated expanding foam), or would this be a terrible idea?

https://www.screwfix.com/p/no-nonsense-fire-rated-expanding-foam-hand-held-750ml/83897

I have considered trying to get pieces of brick in there and cement it, but I don't think this is possible (practical) for me given how tight it is. 

Does anyone have any thoughts, better ideas? Or should I just get a professional to do it because it's not something that a DIYer like me should attempt. Or should I leave it, the house has been here for 90 years (personally I feel it should be sorted, am I wrong)?

Thanks in advance.

Martin_the_Unjust

Personally I would leave it alone, there are plenty of terraced houses of that age and older which don’t have any barriers in the loft.

I would not be using expanding foam as I would be concerned about affecting the roof tiles.

Bendy_House

I wouldn't be concerned about that either, but I can understand why you may wish to sort this as it came up in the survey. I wouldn't get someone in to do it, tho', as it just can't be worth it.

This should be a nice little DIY project for you   That foam is interesting, but my concern would simply be that, unless you leave something there to declare its fire-retardancy, I suspect it'll be highlighted in the future as a 'bodge'!

If access is good - if you can reach these holes easily - then I'd look at sorting it by, say, cutting slightly-oversized hole-shaped card, attaching a cord to its middle, squishing it through, and then pulling it back towards you to make it sit against the back of the hole. Secure the cord with a stick across the front. Repeat for all holes.

Now get a ~5kg pack (depending on the number of holes to fill) of ready-mixed cement, add water to a usable portion to make a stiff mix (one that doesn't slump), and trowel/knife it in there, reasonably firmly, without pushing away the card. 

Perhaps half-fill each hole and allow to set. Then fill flush - it does not have to be pretty.

Unless it's filled with brick or concrete, I suspect it'll always be highlighted as an 'issue', but it barely IS an issue.

GDB2222

Would that be an easier job from the neighbour's side?

If you squirt in expanding foam, from your side, it’s going to make a horrible mess on the neighbour’s  side. 

Can’t you collaborate on this? 

grumbler

Why not simple mortar?

stuart45

Mortar is what I'd use, and stick a few bits of broken brick in stop the slump.
In theory the wall should be flush with the top of the rafters.

rudigarude

Thank you for your responses, I will comment in-line;

Bendy_House said:

This should be a nice little DIY project for you   That foam is interesting, but my concern would simply be that, unless you leave something there to declare its fire-retardancy, I suspect it'll be highlighted in the future as a 'bodge'!

Unless it's filled with brick or concrete, I suspect it'll always be highlighted as an 'issue', but it barely IS an issue.

I think you've highlighted the bigger thing for me, to ensure that it doesn't show up on a future report. I think you're right, along with what some others have said, that mortar is the way forward.

GDB2222 said:

Would that be an easier job from the neighbour's side?

Can’t you collaborate on this? 

I suspect that it may help if I could block one side temporarily to prevent a mess going through, but the main reason I don't want to disturb my neighbour is that her husband recently died.

grumbler said:

Why not simple mortar?

stuart45 said:

Mortar is what I'd use, and stick a few bits of broken brick in stop the slump.
In theory the wall should be flush with the top of the rafters.

You're right, I think I should just carefully try to use brick and mortar. I guess I was doubting my ability to make it look okay along with hoping for a quicker fix. But I should just do it properly.

Thank you all for your comments.

plumb1_2

Spot and dab 1200 mm strips of fire rated plasterboard along the wall 
just use some nails in the mortar joints to hold it while the adhesive sets.

Alanp

Fire retardant foam should be ok, as long as you don’t go mad with it,