Do-it-yourself attic insulation from the inside

Recommendation points

• Preparing the attic for insulation
• We do without counter-grill
• Do I need capital insulation
• We lay and protect the insulation
• Corner connections – what is the specificity
• Subtleties of roof ventilation

The construction of the attic does not end there. If it’s time to insulate – study this material, in it we will provide a list of tips for professional installation and touch on such specific issues as drawing up a roof pie and protecting complex junction nodes.

Preparing the attic for insulation

For the entire duration of the work, it is very important to free up the already not very spacious rooms to the maximum, leaving only the necessary tools and devices. Building materials are best served in the attic as needed..

We go around and carefully study the seamy side of the roof. We sweep away dust, cobwebs, do a complete cleaning of the room. We cover the rafters and crate with an antiseptic from a sprayer, even if the wood has already been treated.

Now you can get to work, but only on condition that the under-roof ventilation is thoroughly thought out and will function as it should. Otherwise, the high humidity will negate all the benefits of insulation, but this time it will not be possible to get rid of the tearing off the casing and re-laying the insulation. When in doubt, look out for ridge fan systems and hinged gable insulation to reduce the risk of failure.

Remember, too, that not all roofing can be converted to suit the purpose of the attic without tearing the flooring. The main limitation is the width of the ventilation gap directly under the roof covering, which ranges from 35 to 100 mm, depending on the slope of the particular slope.

We do without counter-grill

The attic will be insulated in two stages. At the first, all the space between the rafters is filled with mineral wool insulation. Often the developer offers to fill a counter-lattice from the inside to make this layer thicker, but in the case of a thoroughly insulated attic, this does not make sense. The bottom line is that under-roof insulation is not taken into account in the insulation scheme, it is installed only to exclude boundaries with too high a temperature difference, where condensed moisture usually forms.

A layer of under-roof insulation is made with a thickness of 100–150 mm with an inward displacement. Usually the thickness of the rafters is 200-250 mm, so the remaining space is more than enough for ventilation. The thickness of the ventilation layer must be respected without fail, even to the detriment of thermal insulation.

In practice, this is not difficult to implement: distance slats are nailed in the corners between the rafters and the roof sheathing, the thickness of which is equal to the ventilation gap. A bounding plane is mounted on these slats, use a plastic garden net, shingles or thin wire stretch marks for this. The insulation does not need to be fixed thoroughly, it is much more important to distance it from the waterproofing under the roofing.

Do I need capital insulation

The attic is not always arranged as a living space. If we are talking about a warm attic, then all further efforts are reduced to sheathing the room from the inside with particle boards or fiberboard directly along the rafters.

If the attic needs to be really warm, there is one trick to do. Its essence is to create a separate insulation circuit inside, separated from the under-roof by a deaf hydro-barrier. For its device, thin (15–20 mm) slats are horizontally pierced along the rafters with an axial pitch equal to the width of the roll material. It is on these slats that horizontal rows of film are glued and high-quality fixation. The common technique of sealing with aluminum tape does not provide sufficient reliability.

The water barrier is covered with OSB or plywood sheathing; during installation, you need to outline the installation locations of the rafters. In the Mauerlat area, vertical supports are mounted to the rafters. They should form a vertical plane that is a continuation of the enclosing walls. By shifting this partition inward, you can make the attic warmer at the expense of the usable area and overall heat loss at home. The resulting wedge-shaped cavity is filled with scraps of under-roof insulation.

1 – roofing; 2 – roofing film; 3 – rafters; 4 – vapor barrier; 5 – OSB boards; 6 – insulation

Further, a frame is mounted on the sheathing plane, which is attached through to the rafter beams. You can give preference to an inch board 50, 80 or 100 mm wide for the thickness of the mineral wool used. Boards are installed horizontally on the edge and secured with steel corners.

It is also possible to use rack-mount profiles for gypsum board of a range of 50 mm. The first row is packed horizontally, all subsequent ones are perpendicular to the previous one. With this installation, the direction of laying the insulation changes, which means that solid bridges of cold are excluded.

We lay and protect the insulation

For insulation of the attic, it is not recommended to use polystyrene or expanded polystyrene plates. The best performance has a foam glass contour, which, however, can be successfully replaced with mineral wool. Its density must be high enough for the material to keep its shape..

Before laying the insulation, walk with a cylinder of polyurethane foam through all the cracks and joints of the cladding, pay special attention to the corners at the gables, the outer corners on the valleys and the abutments of the roof windows.

If the frame is multi-row, the insulation should be laid in stages. After installing the insulation, it must be covered with a two-layer vapor barrier, gluing it along wooden slats or a profile, no scotch tape and fastening with staples. As a result, you get an internal heat-insulated capsule, guaranteed no moisture leaks under the roof and a reliable frame suitable for plasterboard, OSB or any other material.

Corner connections – what is the specificity

Before proceeding with the interior decoration, make sure that the insulation is installed in a continuous loop. When purchasing high-density cotton wool, you will encounter the difficulty of curly trimming, and too soft insulation will break down and settle over time. It is best to use stone wool 60–100 kg / m3. It is not difficult to join and small gaps are easily filled with polyurethane foam.

Of the more challenging sections, you are likely to come across:

1. Transition from flat ceilings to sloped walls.
2. Pairing wall insulation with slopes.
3. Adjoining sloped walls to the solid glazing of the pediment.
4. Joints between dissimilar materials.

Subtleties of roof ventilation

Airing insulation under the roof is a topic for a separate conversation. However, the basic principles and physics of processes are extremely simple..

The most effective scheme is considered when the supply air enters under the roof through the eaves or Mauerlat. Air movement occurs naturally due to gravity. Naturally, the greater the deviation from the vertical, the more difficult it is for air to pass through, which means that the gap should be larger.

The ventilation outlet is located in the ridge area. Usually, a so-called “cold triangle” is arranged in this area and aerators are installed. It is important to remember that indoor areas are the main source of moisture, especially if there is a bath or shower, or constant drying in the attic. Therefore, it is necessary at all costs to prevent the penetration of moisture with a solid barrier and correctly space the waterproofing into two zones, avoiding conditions under which condensate can form and accumulate.