Ventilation pipes through 220 mm rafters, load-bearing capacity maintained?

[1903]

It would be pleasant to drill through multiple rafters to install ventilation pipes of 100 mm. The question is whether this affects the rafter enough for it to be impacted by this? Half of the material disappears in one place, leaving it 6 cm "thick" above and below. It becomes like a Grevé cheese...

Can you drill 105 and insert an iron ring or something?

Or no problem?

 

[basseman]

Picture? Is it possible to reinforce with a beam above and below the hole?

 

[Janus82]

Removing half of the roof truss can never be a good idea. Even though a lot was over-dimensioned in the past, it can't withstand such large alterations. Either you need to reinforce the truss or you have to find another way to route the pipe.

 

[Finndjävel]

You can't imagine reducing the ventilation pipe to 80mm?
In theory, you could take a piece of a DN80 steel pipe and slit it, i.e., cut away about 8-10 mm along the length. Then make a hole in the roof truss that is a few mm smaller than the outer diameter of the steel pipe. Then compress the pipe enough so that it can be tapped into the hole. Then expand the pipe so that the force is evenly distributed around it. It shouldn't become much weaker that way.

 

[useless]

Several smaller pipes in parallel perhaps?

 

[Daniel 109]

Finndjävel: What forces do you imagine the ring should absorb? I don't see it being of any use.

 

[Finndjävel]

Finndjävel: What forces do you imagine the ring will absorb? I don't see that it serves any purpose.

Imagine that the hole you drill is like a large knot hole. As long as the knot is fresh and held in place, it's stronger. When it falls out, it becomes weaker.

 

[useless]

The beam is primarily meant to handle tensile forces. It becomes worse at that if a tube too large is pressed into the hole.

 

[Jarlingar]

Screw and glue a piece of 15mm plywood on each side of the rafters, say 60cm long and the same width as the beam.

Then you can drill your holes.

 

[Daniel 109]

No, it is not. The tree compensates for the branch when it grows. But a dried branch does not add any load-bearing capacity on its own.

The underframe of a truss primarily takes tensile loads, that ring does not help at all in that situation.

 

[Stefan1972]

It probably also depends a lot on other conditions; a house likely won't collapse just because you drill holes if there are other walls that the rafters rest on and are attached to, but if they are free-standing rafters, you might be tempting fate. If you absolutely have to do it, then I would probably fasten 50mm flat bar above and below that extends a meter perhaps, so you get some anchoring points. Maybe even on both sides and use through bolts and nuts.

That ring that was mentioned is, as stated, of no use whatsoever. The load on the rafter is, as already mentioned, a tensile load from the walls.

 

[1903]

THANK YOU for the input. The consensus is that too much material is being removed. Reinforcement cannot go over or under, as the ceiling and floor are flush. However, one could place two beams, one below and one above, that are as high as the remaining material, like 45*45. Or drill smaller holes and multiple pipes as useless suggests. The ring will be tricky. If a ring, it should be hammered in with force to counteract compression? Like a church tower.

 

[Finndjävel]

You don't need a beam to handle the tensile load either, do you? A regular board is enough. Did you think that the outer walls and snow weight would create such a large tensile load that the beam would be pulled apart in the middle? It's probably more the deflection that's countered if you insert a pipe. The pipe corresponds to a fresh branch, not a dry one.

 

[Daniel 109]

Those look more like they are sized as floor joists. As mentioned, it's primarily deflection that is the determining factor.

 

[Finndjävel]

However, you could place two beams, one below and one above, as high as the material allows, like 45*45. [bild]

Place a piece of plywood (like 22x100cm) which you screw-glue where you want the hole. Do this before you drill and drill through both.