How to make a ventilation and chimney passage through the roof

Recommendation points

• Roof systems and chimney configurations
• Placement: what you need to know
• Unloading the roof
• We cut an opening in the roof
• Ventilation ducts, cuts and cuffs for them
• Chimney lining – we do it safely

Today we will try to figure out how one of the most difficult junctions is performed correctly – the passage of technological pipelines for the chimney and ventilation through the roof. No wonder that many ways have been tried for this, the best of which we will share with you.

Roof systems and chimney configurations

The passage of the chimney through the roof can be carried out with almost any slope of the slope, with the exception of pyramidal and folded roofs with an angle of more than 70 °. Restrictions are imposed for the most part by the common forms and standard sizes of special fittings for insulation – roof chimney cutting.

The exit of the pipe to the roof should be located on a flat slope, at least 1 meter away from the ribs and valleys. Firstly, this is the only way to properly mount the apron and lining, and secondly, no serious interventions in the rafter system are required.

If ventilation ducts can be conducted through the roof with a minimum layer of lining, or even without it at all, then the chimneys need additional thermal insulation from the roof cake. We will touch on this issue later, for now you need to make a choice between a circular and rectangular section of the well. A well made of brick can be quickly and efficiently through the roof; it has the most suitable geometry. In one well, you can group both ventilation pipes and a chimney.

A round passage is also possible, but for the chimney in this case, a casing pipe with a diameter of 350-400 mm larger than the chimney is required. Difficulties arise in fixing it in the roofing pie, besides, not every roof cut has a sufficiently wide cuff.

Placement: what you need to know

It is optimal if you are building a rafter system with already installed wells and pipelines, however, the sequence of work may be forced to change.

If the channels have already been installed, it remains only to correctly assemble the frame system. The rafters closest to the pipelines should be 50–70 mm away from the ventilation ducts; they should be removed from the chimneys by 200–250 mm. During the heating season, the heat radiation from the chimney is large enough to cause uneven wood shrinkage and warping. Change the pitch of the rafters and do not be afraid to place pairs of trusses closer to the design distance.

It is better to place the chimney 15–20 cm from the upper ridge: this way the protrusion of the chimney above the roof will be minimal and there will be no difficulties with sealing the upper part of the cut. Decide for yourself how to implement this: build a well as close to the ridge as possible or make the roof slopes uneven and bring them right above the chimney.

Unloading the roof

If you have to violate the critical elements of the rafter system, which can happen if the step of installing the rafters is less than the thickness of the well, it is necessary to unload the roof. At 40-50 cm from the upper and lower boundaries of the passage, horizontal beams with a length of 5-6 spans should be placed under the rafters. They are propped up by vertical posts so that each of them is located strictly above one of the beams of the attic floor.

With the help of a plumb line, the attachment points of the vertical racks are marked, taking part of the load from the rafters. Each of the broken rafters must be propped up in two places – above and below the cut area. If there is a brick well, it is better to unload the rafter system on it, replacing part of the wooden racks with angled steel bevels.

Even if the opening fits between the rafters, they should be pulled together with horizontal jumpers of the same width, forming a convenient pocket for laying the insulation belt. Sometimes, for reasons of economy of material, it makes sense to install vertical jumpers at the same distance from the pipe or well..

We cut an opening in the roof

If the construction of the rafter system and the rest of the installation steps are carried out with a well or pipes laid out, the opening is formed as the roof is assembled, which in most cases does not cause difficulties. If you need to cut an opening in an already finished roof, you should follow a certain procedure:

1. The roof is unloaded and all necessary lintels are installed.
2. Lintels that form a pocket for thermal insulation are installed at a distance from the ventilation pipes equal to the thickness of the roof insulation.
3. The walls of the duct for non-lined chimneys are installed with an indent of 200–250 mm. For brick wells and insulated sandwich pipes, the lining is performed similarly to ventilation.
4. The profile of the through opening in the shape of a pipe or a well is transferred to the crate using a plumb line.
5. If the roof covering is not resistant to high temperatures, it is cut exactly around the perimeter of the pocket..
6. Almost any coating can be cut well with an electric jigsaw or a reciprocating saw, if you first screw the cut pieces of the crate to it.
7. The indentation from the walls of the pocket allows you to cut the coating from the inside, but if the cutting is carried out along the perimeter, you can transfer the markings to the street using through holes at key points.

As a result, the roof is ready for pipe installation or further protection from moisture and heat leaks. The specific method of arranging the passage channel depends on its type.

Ventilation ducts, cuts and cuffs for them

Ventilation passages for a cold attic space may not be insulated at all, it is enough to make a neat hole in the insulation, lathing and roof. But if warm air from a house or attic passes through the pipes, an imbalance in temperature can lead to condensation. For this reason, it is necessary to lay a small belt around the pipe made of a moisture-resistant material such as PPS or PU foam. The belt is cut into two equal parts and inserted into a pocket on both sides of the pipe and secured to polyurethane foam. She also needs to close up the seams and cracks, and then sew up the pocket with plywood, cutting it out in the same way and placing it perpendicular to the insulation.

On the front side of the roof, a roof cut is installed for the appropriate pipe diameter and slope angle. Most are installed over the roof, some may require a simple trimming and sealing with sealant.

Chimney lining – we do it safely

After installing the chimney, the opening in the opening is lined from below with a fine steel mesh. If the pipe is round, a galvanized steel strip is attached at four points of the opening, forming a casing sleeve. You can avoid this stage by filling the entire pocket with thermal insulation, but this will take more material: the insulator must be packed tightly. It is recommended to use foam glass or stone wool 120 kg / m2 for lining the chimney³.

The advantage of a casing sleeve is a smooth and neat oval hole in the roof, convenient for laying insulation and tightly covered with a cut. For round chimneys, galvanized steel cuts are used.

Rectangular wells should be refined from the outside with prefabricated aprons. Special cases for chimneys of various shapes are quite common, their main task is to prevent oblique rain from entering the place where the neck adjoins the well.