Advice for the realization of a wooden house extension in Provence

[Coati84]

Hello,

After a long time of reflection, I am choosing an architect in order to file a building permit by the end of May 2021 concerning the realization of a horizontal extension in wood frame of my house built in 1962 in Pertuis (Vaucluse) and made of concrete blocks.
A first outline was drawn up in 2016 but I was unable to follow up for budgetary reasons.

My project will be the following:
- creation of a concrete slab located between the north facade of the house and the garage,
- implementation of an extension of a living area of ​​approximately 40 m² on this slab created with wooden framework, HD rock wool insulation and wood exterior cladding,
- establishment of 2 children's bedrooms, a bathroom (Italian shower, double sink, separate toilet), creation of a kitchen area and an entrance door to the extension,
- modification and upgrading of the wastewater evacuation network of my house following the installation of the concrete slab necessary for the wood extension.

Here are my questions:
• Are a structural study (concrete slab / structure) and a soil study recommended during this study phase?
• Do I take risks of building a wood extension in Provence with a hot climate in summer and possibly cold in winter?
• Are there any regional particularities to be observed?
• I would like to receive advice on the types of wood frame, the types of wall insulation, the roof terrace (parapets, aluminum cover, membrane, etc.), the overall costs per m² depending on the level of finish out of water, out of air?
• I hesitate in choosing a wood siding between red-cedar, chestnut, treated Douglas-fir or an exotic wood, in particular for aspects of durability and lack of graying. What do you recommend for the PACA region? Is the durability of the cheaper Douglas pine satisfactory?
• Concerning the foundations, I hesitate between the solutions "continuous footing with ventilated crawl space of 60 cm" or "blocks (80 to 100 cm) and concrete beams". What do you recommend ?
• Do I take a risk of not installing a crawl space and of passing part of the refurbished wastewater network under this extension?
• The part where the extension will be located is currently wet. What is the best technical recommendation for making an insulating floor?
• I intend to set up the roof solution in steel trough (3% slope) with aluminum cover. What are the best sealing solutions? How to manage the connection with the north wall of the existing house? Does this choice seem wise? How to achieve the waterproof junction with the slope of the roof of my garage including Roman mechanical tiles?
• Do I have to make a wooden frame wall (and expansion joint) adjacent to the north wall of my house or can I do without it?
• Does the choice of HD rock wool insulation appear to you to be a good technical and economic compromise or is wood wool in the same price range?

I am enclosing the plans and associated sections of the sketch of this wood extension dating from 2016 and which will be completely taken over by the architect that I will choose in the 1st quarter. What do you think ? Do you have technical and / or aesthetic suggestions?

I hope that my questions and our discussions will be of interest to a lot of people on the forum. Thank you in advance for your help.

Note
This wood extension project follows on from the major renovations of my house in the 60s carried out in 2011. See also: heating-insulation / advice-for-the-extension-of-my-house-t12235.html

[Coati84]

Hi,

After a certain time of silence, I come back to tell you that I signed this day with the architect with a service concerning the "building permit (DPC)" and "General Design Project (PCG)" missions. The architect I retained had an experience in wood frame extension. The calendar objectives are still to file a building permit by the end of May and to have the work carried out from September - October. A meeting to outline different solutions is scheduled for the end of March.

Do you have any specific advice for me during this design phase with the architect?

As soon as the permit is filed, I will take care of drafting the technical parts myself for the future craftsmen and will choose those who will come to work on the site.

I will have a soil study carried out with a G2-AVP mission and will see with the architect when I start it (budget of around 1.4 k €).

Finally, I will dispense with the structural study.

As a reminder, my extension will be located north of the house. Thus, I should not a priori be afraid of summer overheating due to the sun's rays and I should not a priori necessarily seek the installation of a cross wall. Finally, the exterior siding should age more slowly.

The current design phase is important and here are my questions:

- because of the configuration recalled above, concerning the slab, should I favor a so-called “platform” solution to create inertia with the living space? Or should I create a crawl space that will deprive me of the inertia of the ground? This last solution would make my life easier for connections and evacuations.
In short, I will insulate the slab (joist floor with insulating interjoists?) But should I or no seek to benefit from the inertia of the ground?

- my current choice for the insulation of wood and frame frames is based on HD rock wool. Does this choice seem to me to be a good technical-economic compromise? Do you think that ISONAT cellulose wadding or wood wool can compete economically?

- the more I advance, the more I hesitate in choosing the cladding (about 70 m²) between wood species such as red-cedar or ipe, especially for aspects of durability and absence of graying or fiber panels. wood / cement type VIROC. What do you recommend for the PACA region? I have been very careful lately with the wooden extensions that I see in the Luberon and really see cladding that is aging very badly! It is therefore a substantial budget that I am ready to put on wood cladding or more simply to orient myself towards wood fiber / cement panels of the VIROC type or fibro-cement panels of the ORNIMAT and / or TRESPA type. What do you think ?

-Concerning the heating, I really hesitate between 2 solutions:
* installation of a pellet stove in the living room of my house given that there is currently an unused casing with ducts connecting to the wood extension. This solution seems interesting to me but requires substantial work in our house.
* reservations for the installation of 2 or 3 electric radiant and / or inertial radiators in the extension.

I must reread the 2 books of JP. OLIVA “bioclimatic design” and “ecological insulation”. I was inspired not to design an ecological house but to carry out some energy saving work for my house in 2011:
- replacement of all wooden windows by aluminum windows with double glazing, argon gas, low-emission layer and solar factor of 0.63,
- insulation of roof spaces lost by blowing rock wool to a thickness of 315 mm,
- installation of a humidity sensitive ventilation type A,
- installation of a gas condensing boiler with class VII remote controlled room regulation,
- installation of a pergola in front of the "south" facade with microperforated fabric allowing a cast shade,
- installation of cat flap tiles on the roof to avoid summer overheating,
- ...
I must reread these 2 books to see what I can implement as recommendations on this wood extension.

Thank you in advance for your always constructive opinions and your feedback. Do not hesitate to contradict me or to guide me on new avenues of reflection.

[Coati84]

Hi,

Here are my questions for tonight:

- Is it preferable to submit the summary file prepared by the geotechnician in the building permit file? Can this prevent me from having to ask for additional documents from my town hall's town planning department? Or finally, there is no calendar link to be made between the date of filing of the building permit and the date of submission of the geotechnical expert's summary file.

- As part of this extension project, I will take advantage of the northern property line to make a base wall with associated wood cladding. What do you think of the type of fence below because I intend to be inspired by it with a reasonable height of 1.75 m (cinder block base with rubbed plaster on a height of 80 cm and cladding boards on a height of 95 cm)?

There is currently on this northern property line a row of breeze blocks, a priori positioned in the right place. Can I do without an expert surveyor and ask the town hall to confirm the correct location of this boundary which faces a public street?
To be honest, I received an estimate of 3k € for a simple demarcation of my plot of 670 m² with very easy access and that seems to me very excessive.

- Concerning the foundations, my architect is in the process of finding out about the installation of screw piles, the dimensioning of which would depend on the soil study. What do you think ? It may sound appealing to me. Do you think that this solution can be a techno-economic optimum? Do you have a price order for a footprint of approximately 45-50 m²?
Even if I am a priori carried on a concrete slab, in the hypothesis of screw piles, could I consider a load-bearing wooden slab?

- Regarding the choice of insulation, the technical selection criteria are the R and the associated thermal phase shift. I am still oriented towards HD stone wool but my choice could be wood wool if the latter were more economical.

- Concerning the cladding, I discovered the Vibrato false openwork cladding (Douglas fir class 3b from Limousin) from the PIVETEAU brand. This brown or gray colored siding by impregnation looks really superb and seems to resist over time. Has anyone ever installed this type of siding in the south of France and could share their experience? The price of the supply per m² is high and is around 78 € / m². I think that the cladding of my future extension will not gray much because it is located due north and will receive only a few rays of the sun except the very small part facing south (about 1.70 m).
I have received samples of TRESPA fiber cement panels. What is the aging over time of these fiber cement panels? I saw EQUITONE TECTIVA fiber cement panels with Carbon and Taupe colors on a construction site and I found them superb. Do you have any feedback on this EQUITONE brand?
Finally, on this subject of cladding, my architect told me about Accoya wood, that is to say treated with an acetylation process. Has anyone already installed this type of wood in siding? Is there a very long period of absence of aging for these Accoya woods?

- For the heating system and due to rentals planned from 2022, I am thinking of moving towards an independent heating system. It seems to me that with the excess insulation on the floor, exterior walls and ceiling, an electric towel warmer and an electric radiant heater placed centrally in the extension should be sufficient and be the best economical solution especially since j hope I don't need to heat up.

- Last week I met the manager of a company specializing in timber construction who told me that it was useless to make a wooden frame wall along the north cinderblock wall of my house. Sounds okay to me. What advice do you give me on making an extension with 3 or 4 walls? In the absence of a 4th wooden frame wall, are there any precautions to take regarding humidity in particular at this specific location of the north cinderblock wall of my house and the possibility of free expansion?
In the case of a school where there is no timber frame wall along the north cinderblock wall of my house, should the horizontal studs of this wall and the roof rafter be fixed or should it also be fixed? slab belt beam in contact with the north wall of the house? My intuition would make me say that I must separate my house and the future extension. How to technically achieve this separation without putting in place a timber frame wall along the north cinder block wall? I find it difficult to get clear answers on this subject.
Finally, should we prefer assembly on site or in ready-to-assemble kits with prefabrication of the frameworks in the workshop? Or ultimately, it doesn't matter and it's the quality of the carpenter / roofer that matters.

Thank you in advance for your always constructive opinions and your feedback.

[Coati84]

Hi,

At the beginning of the week, I just validated the very successful sketch drawn up by my architect. We are starting the pre-project study phase in order to be able to file a building permit for this extension which will ultimately have a living area of ​​42.50 m².

Here are my questions for tonight:

- Having validated the final position of the footprint via the sketch, I will bring in the soil study office within 15 days and I will be able to have access to the summary file established by the geotechnician before the filing of the the building permit file. It will help me define the foundations and it does not hurt any more.

- Regarding the foundations, I hesitate between 2 solutions:
1) strip sole with crawl space
2) installation of screw piles, the sizing of which will depend on the soil study.
What would your recommendations be?
The leader for the installation of screw piles is TECHNOPIEUX. Do you know of any competitors?
What is a priori the best technical and economic optimum for a footprint of around 50 m²?
I made my choice and will set up a concrete slab whatever the assumption made concerning the foundations.

- As part of this extension project, I intend to take advantage of the northern property line to make a base wall with associated wood cladding. Insofar as my budget would not allow to finance this wall on approximately 30 m long, can I still leave it on the building permit file and carry it out in approximately 2 years after having recovered a certain amount of money? thanks to future rentals of my extension? Do you advise me instead to file a second building permit specifically related to the resumption of my fences?

There is currently on this northern property line a row of breeze blocks, a priori positioned in the right place. Can I do without an expert surveyor and ask the town hall to confirm the correct location of this boundary which faces a public street?
To be honest, I received an estimate of 3k € for a simple demarcation of my plot of 670 m² with very easy access and that seems to me very excessive. There is currently no terminal and I am in the process of recovering the original deed of constitution of the subdivision and the attached plans.

- Concerning the cladding, I discovered the Vibrato false openwork cladding (Douglas fir class 3b from Limousin) from the PIVETEAU brand. This brown or gray colored siding by impregnation looks really superb and seems to resist over time. Has anyone ever installed this type of siding in the south of France and could share their experience? The price of the supply per m² is high and is around 78 € / m². I even noticed that there was currently a tension on the prices of wood and that this price was going to increase.
I think that the cladding of my future extension will not gray much because it is located due north and will receive only a few rays of the sun except the very small part facing south (about 1.70 m). I have received samples of TRESPA fiber cement panels and am now certain to choose wood siding and not fiber cement panels. During the month of May, I have to take a tour of different timber sites with my architect to ask myself about this choice of cladding. Do not hesitate to share with me your experiences on this sensitive point of a wood extension in the south of France.

- In the end, my extension will be contiguous to the “north” wall of my existing house with a return of 1 m at the level of the “east” wall of my house. Are there specific constructive devices at the level of the concrete slab and / or timber frame walls that will be along these "north" and "east" walls of my house? What are screw technical tips?
I can not do otherwise because I want to avoid entering the limit of 0 to 4 m vis-à-vis the street.

Finally, should we prefer assembly on site or in ready-to-assemble kits with prefabrication of the frameworks in the workshop?

Thank you in advance for your always constructive opinions and your feedback.