Renovation of pitched roofs from the inside
Renovating and (retro)fitting insulation to your roof: everyone’s talking about it.
Is your roof still in good condition and do you already have a proper underroof? Do you value better insulation performance, acoustic comfort, and minimizing summer heat? Is cost a factor? And do you prefer working with sustainable materials?
Then our complete solution "renovation of pitched roofs from the inside" is the right choice for you.
The text on this page was automatically translated. Minor translation errors are possible. In case of doubt, the original versions (Dutch and French) are correct.
Download (Dutch version)
What does our insulation system "Renovation of Pitched Roofs from the Inside" include?
Let’s start with an obvious truth: Every roof is different. Especially in renovations, you can’t just do whatever you want. That’s why there’s no such thing as one single solution for every renovation. It’s important to evaluate step by step whether this interior renovation approach suits your specific situation.
First: what defines a quality renovation?
Across all solutions, one core principle we at ISOPROC emphasize is: Good insulation is more than just a thick layer of insulation!
Wind, temperature differences and mechanical ventilation cause pressure differences between the inside and outside of a building. Even the smallest cracks or gaps in the building envelope allow uncontrolled air exchange. This bypasses the insulation. In winter, this can cause energy loss, reduced comfort, condensation issues, mold, and poor ventilation performance. In summer, the same leaks increase the risk of overheating.
That’s why airtight and windtight construction is just as important as thermal insulation. This principle is central to all our solutions.
Step-by-step towards our solutions
Step 1: Is the interior finishing layer already present and absolutely must be preserved?
- If yes, consider the “renovation of pitched roofs from the OUTSIDE” solution.
- If no, read on.
Step 2: Does your building already have a properly functioning underlay?
- If you don’t have an underlay, the roof tiles must be removed and a new underlay installed. At that point, you can still choose to insulate from either the outside or the inside.
- If you do have a suitable underlay, we offer three insulation scenarios using iQ3 cellulose:
Notes:
- Of course, there are other possibilities and solutions using our products. If they’re not in the brochure, contact our helpdesk. Our experts are always ready to help.
- Don’t forget to contact a certified iQ3 cellulose installer before beginning roof and airtightness works, so they can pre-approve the roof structure to be insulated.
Products used
Depending on the chosen variant, we work with the following products:
- iQ3-celulose insulation
Optionally supplemented with naturheld woodflex insulation, if the underroof is not sturdy enough for blown-in insulation. - iQ3-profil ES
Thickening profiles for extra insulation space, combining surface leveling and compartment creation in a single step. - pro clima INTELLO PLUS
Strong, hydrosafe and airtight vapor barrier for all fibrous insulation materials OR pro clima INTELLO X PLUS, if you won’t finish the attic interior soon and diffused UV light enters via windows. - pro clima glue, tapes en accessories
For sealing overlaps, joints, penetrations, etc.
Example: Creating compartments with iQ3-profil
What are the advantages of our "Renovation of pitched roofs from the inside" insulation system?
Even if the interior finish must be removed, interior renovation is often more affordable than external renovation.
- By placing insulation between the wooden load-bearing structure, you avoid raising the roof edges or replacing gutters.
- No scaffolding needed.
- Ensuring airtightness—especially at roof edges—is usually easier and can often be done by the homeowner.
- Blown-in cellulose insulation is also very cost-effective.
- Since the roofing stays in place, there’s no risk of (rain) infiltration during the work.
- It’s easy to ensure the insulation and airtight layers connect seamlessly with existing or future wall insulation.
- iQ3 cellulose is a locally produced Belgian insulation material that is fire-resistant, acoustic, affordable, and climate-friendly. Its strong lambda value, thermal inertia, and full cavity-filling capability (thanks to its adaptable form) ensure excellent performance, even in complex shapes (e.g. varying thicknesses, ridges, valleys, roof bases,...).
- Achieving airtightness is often relatively simple because the airtight membrane can connect directly to the inside of the external walls.
- If needed, iQ3 cellulose can temporarily buffer a fair amount of moisture, which it can later release again.
- Insects stand no chance: access to the wood is blocked by the exterior underroof and the interior INTELLO membrane. Even if an insect is initially present, it cannot leave due to the filled insulation, preventing reproduction. As a result, untreated wood can often be used.
Option 1: Creating large compartments between rafters when the underlay is suitable for direct insulation.
- Quick prep: the roof structure can be reinforced, leveled, and made insulation-ready in one go.
- Fast installation of the pro clima INTELLO PLUS, possibly in one continuous strip from eave to ridge and down to the opposite eave.
Option 2: Creating compartments using iQ3-profil thickening profiles when the underlay is suitable.
- Easy handling of lightweight profiles with minimal cutting waste.
- Fast installation of the INTELLO PLUS, possibly in one continuous run.
Option 3: Combining woodflex and iQ3 cellulose when the underlay is not suitable for direct insulation.
- Enables effective and safe thermal and acoustic insulation, even with an unsuitable underlay.
- In future renovations, insulation thickness can be increased externally while maintaining hygrothermal safety.
To assess environmental impact, it’s best to use a TOTEM analysis. TOTEM is a tool developed jointly by the three Belgian regions, allowing objective comparison of total environmental impacts of construction build-ups.
TOTEM considers not only energy consumption over a 60-year lifespan but also total impact (CO2 and nitrogen emissions, water and raw material use, ozone depletion, and many other factors) from raw material extraction to the building’s demolition.
We’ve documented this cost-effective “Renovation of Pitched Roofs from the Inside” solution in a detailed guide (only available in Dutch and French version). It includes essential information, connection details, 2D drawings, installation instructions, and practical tips. The document also covers pitched roof renovation from the outside. Download the complete solution below.
Still have questions? Don’t hesitate to contact our free technical helpdesk te contacteren. We’re happy to share our expertise.
All system solutions
Our system solutions combine all of ISOPROC's expertise. They include guidelines, detailed drawings, and coordinated products for an optimal approach to pitched roofs, flat roofs, walls, joinery, etc.
