Chimney Roof Cutout

[Gareth Dunn]

Hi Folks

 

This is my first post on these excellent forums, so here's a hello to you all. 

 

I'm relatively new to narrowboats, made my first purchase three months ago and am thrilled to bits with 'Bob', a 50 foot semi-trad. very much hands=onm, been working on camovervans for years and really enjoy doing work myself.

 

In due course, I'll need to cut a hole in the 4mm roof for a wood burner flue.  Any tips for checking that I'll clear any corossmembers that support the roof ?  Are roof crossmembers standard practice in NB builds ?  I have checked that I will be well clear of the seam welds that join the roof sections. 

 

I'm asking as removing the internal roof panelling to gain visibility will be difficult as it spans  a fitted shower enclosure, tho not insurmountable if needs be.

 

Cheers

Gareth

[Jen-in-Wellies]

Welcome to the forum.

Roof crossmembers are likely. Now is the perfect time of year to find where they are. If you can get some warmth in to the cabin when it snows, their position can be deduced from how the snow melts. At least on my boat!

[BEngo]

Boil a kettle inside the cold boat, adjacent to where you want the flue. Allow the steam to rise for about a minute.   The roof supports will show as lines of  condensation.

 

 

[MtB]

That looks like a Liverpool boat roof to me, or Aintree boats. 

 

With that degree of curvature in the roof I wouldn't worry too much (or at all) about hacking through a roof support to get the flue hole in the right place. 

 

 

[LadyG]

Plan to have stove near the middle, rather than near the forward bulkhead, if possible. You want to be warmish in your sleeping area, and warmest in your saloon. I'm not sure about the kit needed, You could be better to pay someone to drill out the hole, and take his advice, it's an easy job, but you dont want to make a mistake in location. 

PS do not seal the deckhead ie wooden ceiling with fireclay. You may need a circular, metal, 'flange' inside on the deckhead. 

Edited January 4 by LadyG

[agg221]

Not to take anything away from @BEngo or @Jen-in-Wellies' suggestions, the crossmembers do not show up so well if the roof has been lined with tongue and groove in my experience, and if the fitter bonded wooden laths in first to make it possible to fit the tongue and groove with secret nails then there are no visible signs of where the crossmembers may be and there is enough thermal separation to stop the above techniques from working so well. There is also the other matter of where the wires run through the roof.

 

One way around this (which I used) was a cheap USB endoscope; I drilled the pilot hole where I wanted it and then I could poke the endoscope through and check. The odds are that the drill bit will push the wires out of the way, so that was less of an issue. If I had been too close to a crossmember then I could probably have moved by a small enough amount to contain the original pilot hole within the original circle, or at least the trim, so it wouldn't have shown. In the very unlucky event that I had needed to move further than that, all I would have needed to do is put a plug in the hole, trim off flush and re-oil, and it wouldn't have shown.

 

I decided it was easiest to buy the right sized hole saw to cut the circle in the roof, which was done easily with a battery drill, just keeping it running slowly. I used a cheap hole saw from Ebay and it was fine for the job - it would have burned up the teeth if I had run quickly, but the battery drill makes it easier not to do this. I decided it was easier to drill the pilot hole from the inside (taking account of where the handrails were on the outside), and then cut the main hole from the outside. Once through, I used a magnet to clean up all the swarf to stop it forming rust spots on the roof and then I could run the hole saw right down through the insulation and the lining to make a neat hole, which worked well.

 

You may already know this, but in case you don't, a twin-wall external chimney has a big advantage on a tidy looking boat roof, as the outer slots over the collar so the rain runs out, and the inner slots inside the collar so the tar runs back in and not on to the roof.

 

Alec

 

Edited January 4 by agg221

[Gybe Ho]

The cross members can be seen in the photo you uploaded. Tap with your knuckles to confirm.

 

The cross members are surprisingly thin and will be at close centres 300mm or maybe 250 centers and you don't want to cut through one.

Edited January 4 by Gybe Ho

[system 4-50]

Magnet for detection?

On my boat the roof supports were at exact regular intervals which could help in some cases.

[BoatingLifeUpNorth2]

A standard sheet of plywood is 8’x4’ often full sheets are used on roofs, builders tend to use the steel roof bearers to fasten to, hiding the joint with a covering strip, if they’ve used this method start at a covering strip and check about 18”-24” away for pin holes where they’ve fastened the board to the next bearer. If you can find the securing pins, you can measure the bearer distance and start roughly working the distance of the bearers out.

 Another way is go in the roof lining from your mushroom vents inside the boat and locate a bearer with a flexible wire cable access rod, then work out the spacing.

 An easy way to cut the hole in the roof, is draw required diameter for the roof collar to be inserted, not flue. Drill a series of 10/12mm holes around inside the line and just jig saw hole to hole following the line. 

 

Edited January 4 by BoatingLifeUpNorth2

[Gybe Ho]

13 minutes ago, BoatingLifeUpNorth2 said:

A standard sheet of plywood is 8’x4’ often full sheets are used on roofs, builders tend to use the steel roof bearers to fasten to, hiding the joint with a covering strip, if they’ve used this method start at a covering strip and check about 18”-24” away for pin holes where they’ve fastened the board

 

 

In addition, for another clue, tease out a ceiling downlighter and poke around in the shallow void above. Be gentle with the ply around a downlighter hole particularly if a varnished ceiling liner panel because the ply could be thin 6mm ply and you don't want to tear off a shard of varnished ply veneer.

 

For less than £20 from screwfix you could buy an electrician's feeler mouse probe thing (they have an odd proper name) and explore through a downlighter hole. Don't assume cabin side metal reinforcement aligns with cabin roof stiffeners.

[canals are us?]

 You may be able to take the ceiling ply lining down as you need access to around the flue to tighten up the bolts to the cast iron collar.  I used high temp silicone and bolted the cast iron collar to the roof.  I cut out a square in my ceiling and then fitted a fireboard cover plate after fitting the stove and flue, plus removed the spray foam insulation 8 inches away. If a decktite/ rubber type seal then, no access below needed as fixings from above.

 

 

James.

Edited January 4 by canals are us?

[Ray T]

Not internal but external. One of my peeves is a non vertical chimney, it doesn't look "right" to me.

When we had a retro fitted wood burner in our boat I had this hardwood spacing piece made up, never had any problems. 

As mentioned above the chimney is double skinned, the void being filled with fire retardant foam.

 

Edited January 5 by Ray T

[LadyG]

I would query why a fire retarded foam is a good idea. With these very short  chimneys, getting a good draught is not easy.

I suppose you might want to protect some fancy outer skin from heat,?

Just now, LadyG said:

I would query why a fire retarded foam is a good idea. With these very short  chimneys, getting a good draught is not easy.

I suppose you might want to protect some fancy outer skin decoration from heat,?

 

[David Mack]

7 minutes ago, LadyG said:

I would query why a fire retarded foam is a good idea. With these very short  chimneys, getting a good draught is not easy.

Insulation keeps the flue gases warm which encourages them to rise up the chimney i.e. improves the flue draught.

[jonathanA]

Usually the cheaper twin wall chimneys have an inner that is often a poor fit to the boat flue, leaving a gap that flue gases can go.up resulting in gunge leaking out of the chimney collar.  Shoving a bit of insulation up there helps prevent/reduce that in my experience. I doubt it makes much difference to the draw of the overall flue. 

[blackrose]

16 hours ago, MtB said:

That looks like a Liverpool boat roof to me, or Aintree boats. 

 

With that degree of curvature in the roof I wouldn't worry too much (or at all) about hacking through a roof support to get the flue hole in the right place. 

 

 

 

It's definitely easier if you don't have to hack through a cross-member. 

[Tony Brooks]

4 hours ago, jonathanA said:

Usually the cheaper twin wall chimneys have an inner that is often a poor fit to the boat flue, leaving a gap that flue gases can go.up resulting in gunge leaking out of the chimney collar.  Shoving a bit of insulation up there helps prevent/reduce that in my experience. I doubt it makes much difference to the draw of the overall flue. 

 

FWIW, I slight;y overfilled mine, then put a couple of layers of aluminium foil over the foam, and while the foam was still soft shoved it into place. This ensured the aluminium foiled foam touched the stove flue to make a reasonable seal - I had that gunge on roof problem with the previous double skin chimney.

 

I have heard of people filling the space between the inner and outer with scrunched up aluminium foil, but I can't see that helping much to keep the inner liner how to minimise condensation forming on it.