Basic rules for insulating pitched roofs

The construction of a private house is accompanied by an understanding of the whole system of “little things”, each of which affects future comfort. This time we will talk about the thermal insulation of the roof. Of course, the easiest way is to entrust all the work on the design and installation of insulation to specialists. However, the knowledge of the basic rules and possibilities does not hinder the real owner, it is much easier to detect the mistakes of builders in the early stages, when their correction has not yet passed into the category of “building anew”. In addition, the insulation of the pitched roof is not so difficult to understand, many craftsmen generally make it with their own hands.


  • Why even insulate the roof?
  • How to insulate a pitched roof – theory
  • Selection of materials
  • Waterproofing, it’s also windproof
  • Insulation for pitched roof
  • Vapor barrier

Why even insulate the roof?

People far from construction may not be aware of the importance of roof insulation. Nevertheless, thermal insulation is really necessary – both to reduce the cost of heating the house (so that most of the heat does not go to the sky), and to make it possible to equip the attic living room, and to increase the durability of the roof itself (that is, all the elements involved in its creation ) And if heat loss through the roof and the residential attic do not need comments, then here’s a little more detail about the effect of insulation on durability. With a “bare” insulated roof, we get this kind of picture:

  • the roof has an outside temperature, that is, in the winter season from 0 to minus 20-30 degrees;
  • in the house itself, the air is warm and humid, and this air tends to rise (the laws of physics know everything);
  • meeting with a cold coating, the air cools, and the moisture from it condenses on the beams, rafters and other roofing materials.

In total, we have constantly wet roof surfaces, which leads to wood decay and corrosion of metal parts. What do you think – how long will the roof last in such conditions? So warming is a must!

How to insulate a pitched roof – theory

Correct roof insulation is the installation of the so-called heat-insulating “pie” of several layers that perform various functions. The main elements of the “pie” are (bottom to top):

  • the inner lining of the attic attic
  • air gap
  • vapor barrier film
  • insulation
  • air gap again
  • moisture and moisture protection with sufficient vapor permeability
  • and again the air gap
  • external roofing materials
Basic rules for insulating pitched roofs

Layered arrangement of thermal insulation elements

The general outline is surprisingly simple, isn’t it? And almost anyone can follow to ensure that the project is consistent with the foregoing.

Selection of materials

Theory is theory, but it’s time to move on to practice. And first of all, you need to select all the necessary materials, tracking not only the prices and quality, but also the compatibility of the elements. Consider the main options for materials of all three categories: hydrobarrier, insulation and vapor barrier.

Waterproofing, it’s also windproof

When choosing a material for waterproofing, it should be clearly understood what characteristics it should correspond to. So, a reliable hydrobarrier should:

  • retain water, preventing it from seeping in, to the heater;
  • let steam from inside out, which could pass through a layer of thermal insulation;
  • possess sufficient strength and elasticity for long-term operation;
  • maintain their properties in a wide temperature range (from about -40 to + 40 ° C), as well as when exposed to wind and ultraviolet radiation.
Basic rules for insulating pitched roofs

Wind and moisture protection – “breathing” diffusion membranes

Before you go to the procurement, it is worthwhile to consider in more detail the various moisture protection options that are currently available on the construction market. The following species are considered the most common (in increasing prices):

  • rolled ones – with a dozen varieties of roofing material, of which euro- and glass-roofing material are more and more popular, as they can be easily docked tightly due to the possibility of tightly melting seams (joints);
  • film – a lot of variations related to two categories: polyethylene and polypropylene (they are most often called waterproofing), and in the second case, when laying, you need to carefully monitor the correct orientation of the moisture permeability of the sides, but – a bonus – in modern films at the edges often is already present double-sided tape, which is convenient to fasten the panels;
  • diffusion membranes – “breathing” materials that allow moisture to pass only outward.

All the materials presented are consistent with the above characteristics, well, plus or minus. So choose based on your requests and wallet.

It should be remembered that when installing the hydrobarrier, tightness is important – the material should envelop the rafters, and between them it should be attached with a slight sag (maximum bend – no more than 2 cm at the lowest point)

Insulation for pitched roof

For the insulation, we also give the necessary functionality. High-quality thermal insulation material should have the following qualities:

  • low thermal conductivity, due to which heat is stored inside the house (the lower this indicator, the thinner the insulation layer is needed);
  • the ability for a long time (that is, until the end of the useful life) to keep in shape;
  • optimal density – a heavy insulation under its own weight quickly enough kneads, losing its useful qualities;
  • resistance to temperature extremes;
  • fire safety;
  • environmental friendliness – the insulation must be chemically resistant and biologically inert both in the normal state and when heated;
  • the duration of the service life (while maintaining all the useful characteristics)
Basic rules for insulating pitched roofs

Insulation for pitched roofs – basalt wool

In principle, there are a lot of materials that meet all the specified properties, especially if you take into account different brands. However, most often in the attic thermal insulation of the roof, two categories of insulation are used:

  • mineral (basalt) wool
  • fiberglass

Both thermal insulation are produced in rolls and plates, the width of which corresponds to the standard inter-railing distance. Therefore, the calculation and laying of insulation is the easiest stage in the formation of the roofing “pie”.

It should be remembered that the installation of heat-insulating materials is carried out in such a way that there are no gaps between the supporting structures and the insulation – the tightness of the fit will eliminate the formation of cold bridges

Vapor barrier

The requirements for vapor barrier are very similar to those indicated for the hydrobarrier, with the exception of one item. The vapor barrier material must comply with the following characteristics:

  • if possible complete moisture and vapor impermeability;
  • high strength;
  • sufficient elasticity;
  • annual temperature stability.
Basic rules for insulating pitched roofs

Vapor barrier materials

Many believe (and not without reason) that an ordinary dense polyethylene film in its quality fully corresponds to the above list. Still, I want to expand a little bit of information about vapor barrier. So, modern science provides a good selection of membrane materials:

  • with a reflex (reflective) layer – has increased vapor and heat resistance, therefore it is most suitable for use in apartment-type attics (with living rooms, a kitchen and a bathroom)
  • with limited vapor permeability (steam transmittance (Sd) in the range of 2-4 m) – differs in diffusion ability, which makes it possible to get rid of residual moisture in rooms where there is no constant vaporization (that is, in which people do not live permanently)
  • with variable vapor permeability – changes the ability to transmit steam depending on moisture (from Sd = 5 m in the dry state to Sd = 0.2 m in the wet), which allows not to make an air gap between the membrane and the inner lining of the attic

Now you can choose the kind of material that will best suit exactly your desires, so go for it.

It should be remembered that the vapor barrier (as well as moisture protection) should be as tight as possible, therefore, the material must be fastened across the load-bearing elements close to the insulation, and the panels must be laid on top of each other with a minimum overlap of 10 cm and glued with the most convenient accessories – double-sided tape, glue or duct tape

As promised – nothing complicated. But now you can easily control the work of roofers-designers or even independently install the roof insulation. Successful building routine!