Toiture avec isolation extérieur sur base de panneaux KLH

[chouchen29]

Bonjour,

Je réalise actuellement un calcul sur une toiture de type KLH, avec isolation extérieure en laine de roche et membrane d'étanchéité type Elastophene.
les résultats du calcul indiquent une accumulation d'humidité rapide et forte dans les premiers centimètres d'isolant sous la membrane d'étanchéité. En deux ans la teneu en humidité dans ces premiers centimètres de laine de roche passe de presque 0 kg/m3 à plus de 300 kg/m3.

Voici la structure de l'intérieur vers l'extérieur : KLH 95 mm / pare vapeur delta fol aevc sd 20m /lame d'air de 60 mm/ panneau OSB de de 18 mm hydrofuge / laine de roche lambda 0.039 en 300 mm / membrane elastover / membrane elastophene 25.
Pente 3 à 5 %, orientation nord, localisation à Saint-Brieuc (dpt 22 en France). Usage du bâtiment : Collège.

J'ai fait des variante avec la membrane (delta fol Sd 20m / vario / pare vapeur avec Sd 100 m) : pas de différences notables dans les résultats des calculs. Idem en faisant varier l'épaisseur de la lame d'air.

Il y a t-il une conception inadaptée de la paroi ?
Ai-je fais des erreurs dans la codification de la paroi ?
Je peux vous envoyer mon fichir WUFI

Merci des réponses que vous pourriez m'apporter
Pascal BROCHEN

[Christian Bludau]

Hello Pascal,

if you add the sd-value of the KLH to the vapor barrier, you get a sd-value of about 30m at the inside. There the moisture can not really try out. Same case with the other barriers, they are too tight. The vario is not working as the KLH is to tight. The change of the interior airgap has no influence, thats because the vapor will pass no matter how thick that is. And there is only a low change of the thermal transmission.
Is it a roof or a wall you are calculating? Did you include the radiation? Do not forget to set the absorption and emission according to the surface. For a roof switch on the explicit radiation balance.
Using a vario without the KLH (use gypsum board instead) may help to control the moisture. If not you can add a additional layer of insulation (maybe EPS) to the outside. If you do use an vapor open material for that, you need a tight layer between the two insulation layers...

Regards,
Christian

[Emilie M.]

Hello Christian,

I have the similar problems than Pascal but with a different flat roof composition (as attached picture).

I tried to simulate this roof with two different vapor layers : one with Sd=20m(PE) and this other with a variable Sd value (ie INTELLO).
For the calculations, I chose to inclued radiation and I indicated 0.6 for absorption and 0.9 for emission.

My first question is : Do we need to set Sd value of exterior and interior surfaces if we also created a component layer with them (waterproof layer ans gypsboard).

Do you know why the results are similar with these two differents layers. (same end profile of RH). Which criterion of calculation impact?

thanks in advance for your answer.

Best regards,
Emilie M.

[Christian Bludau]

Hello Emilie,
if you built in the layer you have not to set an sd-value on the surface and vice versa. On the exterior it is better to use the surface sd-value. On the interior side that is not possible, if you like to calculate a variable membrane, you have to build that in.
You get the same conditions in both cases? Did you set the interior heat transfer coefficient the right way? eg 8 W/m²K?
At which position did you look on the water contents?
Christian