Let’s make this clear once and for all: prefab wooden homes are NOT for those who look for cheap or temporary solutions.
Today, prefabrication is the most advanced way to build a house and many luxurious homes are built with this system.
Factory production of houses has gone a long way and we can now benefit from different kind of manufacturing technologies and different types of construction. This has completely changed the way we must look at prefab wooden houses.
This article explains important aspects you should know before attempting to buy a prefab home, including:
- Quality / Energy / Sustainability;
- types of houses;
- types of construction;
- what it consists of;
- how can you build one;
- how do you get started to get one.
...so buckle up, get a cup of coffee (or tea?) and let's get go with it!
1. Quality, Energy, Sustainability
This is why we are addressing the Quality issue upfront.
There are good smartphones and exceptional ones. There also crappy ones.
You can buy the latest iPhone for about 1k or a fully functional low-end device for just 50 bucks.
They both work, they both get the job done… but your expectations (and experience as a user) would be very different.
While you might not go for the super expensive iPhone, you might settle for something in the high-level range, ensuring quality, reliability, durability.
When buying a house you shall use the very same kind of thinking.
You CAN find super cheap prefab houses. In that case, you WILL face problems and frustration. You have been warned.
This article is about those houses that are in the high-level range and, in the same way I would not advise you to buy a 50 bucks smartphone, I advise you to stay at large of anything that seems too cheap or too good to be true.
Factory prefabrication follows a repetitive set of procedures that are optimized to deliver products in the shortest time possible (hence at the best price) and with the highest quality attainable. Factories are really good at this.
If you think about it, our cars are made in factories, our clothes are made in factories, our phones, laptops, bicycles… even our food is made in factories.
Factory manufacturing is proven to be the best cost-effective and quality-effective way to do things.
Why should houses be built in a different way?
Building a house indoor (at least most of its components) guarantees protection from the weather elements and more control.
In order to be suitable for the manufacturing process, the design of the house shall cover details up to the tiniest one. This makes the level of accuracy of the project much higher than a traditional one, thus leaving less room for mistakes and misunderstandings.
Remember that more quality translates directly into fewer problems.
1.2. Energy Performance
In part, this is due to the overwhelming complexity of the topic (even some of the Top Professionals still don’t get it) and in part due to the fact that building an energy-sucking building is cheaper than building a good one.
Modern materials and construction processes make it easier to reach outstanding energy performances at a reasonable price. When building with wood, energy performance comes built in.
Yes, building with wood is more energy efficient than building in bricks or concrete.
Energy classes like A+ or Zero-Energy can be reached without stretching the budget too much.
If the energy class of the house you are just building is lower than A (B, C, …) then you shall probably have a look at your project: perhaps there are architectural inefficiencies that need to be addressed or you should use better building materials.
In practice, reaching 100% brings little or no benefit while it increases costs considerably.
A “regular” prefab wooden house is mostly built with recycled or recyclable materials (wood, insulation, metal parts, …) and its carbon footprint is very low.
Wooden houses are certainly the better choice for anyone who cares about sustainability.
The factory production also ensures the optimal use of resources such as heating and electricity during the construction works and it also minimizes the waste of materials.
2. The Type of House
Nobody can pick the right type for you, the choice is entirely personal and based on your needs, wants, habits, taste and financial capabilities.
The best way to begin choosing the type of house is asking help to an Architect.
NOTE: if you are going to build a house, sooner or later you are going to need an Architect. It is highly recommendable involving a competent Architect from day one. This will save you headaches, time and money.
Picking one type of house might set certain limitations on what you can do and what you cannot. Limits are given by measurements and performance figures set by local regulations and, in certain cases, by transport issues.
These are the most common types of houses:
- villas or single-family detached houses;
- pair-houses or row houses;
- tiny houses
- micro houses.
2.2. Pair or row-houses
Cabins are generally in the size 60-150 square meters and they have less strict energy requirements than residential houses meant for all-year usage.
Cabins are quite traditional and minimalistic in style.
2.4. Tiny houses
A tiny house is typically one floor (or 1.5 floors) and it has a floor are between 20 and 80 square meters.
Due to the space constraints, every centimeter of internal space is cleverly used. Tiny houses are known for having spectacular interiors.
2.5. Micro houses
Do not be fooled by the micro size (less than 20 square meters)... micro houses are not garden sheds! They are properly insulated and equipped with everything one needs to carry on a good life.
3. The Type of Construction
As a rule of thumb, the more work is done at the factory, the higher the final quality and the most money and time you can save for the works on the construction site.
Here is an overview of the different types of construction technologies and degrees of prefabrication.
Instead of cutting timber on the site, carpenters buy beams that are already cut to measure and all they have to do is assemble those parts in frames.
This method saves some time and some material and it is fairly cheap concerning transport costs.
However, the quality of the build still depends on the skill of the on-site carpenters and the overall construction time of the house is not reduced much compared to a traditional on-site stick-built.
The quality is the same of a traditional on-site stick-built.
This system is widely used in UK and other Countries.
After pre-cutting parts, the factory also assembles them into frames, delivering at the site entire section of walls, roofs, ceilings.
Compared to pre-cut, buying ready-made frames is more expensive and it comes with these additional costs:
- more work at factory, hence higher purchase price;
- higher transport cost (move volume, you need more trucks);
- higher handling cost on site (you need now a small crane).
On the bright side, several days or weeks are saved on site as the skeleton of the entire house can be built in a matter of a few days.
The quality of the build is comparable with a traditional on-site stick-built.
3.3. Element (or panelized)
Not only the frames are factory-built, also insulation is fitted at the factory, together with external cladding, windows and sometimes even electric pipes and internal gypsum boards.
Some factories are able to deliver element walls, roofs, ceilings which are 80% finished in the factory!
Compared to on-site traditional building methods, this saves weeks and it comes with a better quality.
In fact, all the materials are handled and fitted in a dry and controlled environment and there is no space left for last-minute improvisation (typical of on-site carpenter's work).
When you buy a prefab element house, you get exactly what you ask for.
Building with elements is smarter than building with frames.
Additional time (a few weeks) will be necessary to install technical systems and perform interior works and finishes.
Almost any architectural solution can be developed using prefab elements.
If your house has a "weird" geometry, elements are the way to go.
3.4. CLT (Cross Laminated Timber)
Elements can be built using CLT, therefore building with CLT offers pretty much the same benefit of building with prefab timber-framed elements. However, CLT itself is more expensive than timber-frames... so keep an eye on the cost.
In general, designing a CLT structure is faster (and cheaper) than designing the same structure for timber-frame technology.
However, the savings in design usually do not make up for the increase of cost in materials.
CLT offers better structural performance, therefore, it is to be preferred in case there are heavier loads or environmental construction (tall buildings, seismic activity, ...).
Finally, for the same wall thickness, the timber-framed wall will always offer a better energy performance.
For the purpose of this analysis suffices to say that modular construction delivers on-site fully ready "boxes" (ready from outside and inside). On-site work is reduced to a minimum.
Yet, depending on the architecture of the building, some works have still to be performed after the installation of the modules.
NOTE: modules are always built using prefab elements or frames.
Modules take more time (and money) to be designed and more time to be produced.
Oc course, time is saved on-site but the overall length of the project is comparable with element construction.
In all other cases, element construction will be a better solution since it is more flexible and it comes at a comparable price and time of implementation.
4. The Building Envelope
If you are not familiar with the various parts of the house, you risk buying something that does not work for you or, worse, leaving our some important part (i.e. buy a house without a roof!).
- external walls;
Here is a list of additional components (not covered by this article):
- internal walls;
- separation walls;
4.1. Wall Types
When it comes to layers, external walls are the most "complex" element in the entire building. An external wall can count over 10 layers.
Like any other component of the building envelope, the primary functions of these elements are:
- providing structural stability;
- providing protection from the weather;
- providing good energy performance;
- keeping the air inside from leaving the building and air outside from entering uncontrolled.
To serve all these functions, the typical layer structure of an external wall is (from the inside):
a) 13mm interior gypsum boards;
b) 10mm moisture resistant chipboard;
c) 45mm wooden service-frame, fitted with 50mm insulation and electricity pipes;
d) vapor control layer (plastic film or membrane);
e) 195-245mm structural timber-frame, fitted with insulation;
f) 9mm wind-protection boards;
g) wind-barrier (membrane);
h) 28mm wooden vertical battens;
i) horizontal wooden cladding.
An external wall built to these specs ensures superior performance and durability.
Keep in mind that using gypsum boards allow getting the walls closed at the factory while using other materials might force the producer to deliver open walls (i.e. interior wooden boarding has to be installed on-site). This could generate extra costs on-site.
At the same time, you shall take into account that gypsum shall be rendered and painted while interior wooden boarding does not need any treatment.
You have to do the math yourself. Producers will not go into that kind of detail.
The chipboard provides structural stability to the element and makes the wall surface very robust.
A wall with this construction cannot be broken by just smashing into it. If your walls do not have the chipboard layer, the interior surface can easily break.
On top of that, you can easily screw accessories on the walls (shelves, cabinets, ...).
the benefits provided by this layer are enormous and it really does not make any sense to omit it.
This layer is usually omitted in any cheap constructions.
To make it very simple: do not buy a wall that does not have this layer!
The service frame allows pipes to be laid inside the interior space of the house, effectively reducing the risk of air leaks which always happen when pipes penetrate the vapor barrier (d).
When a service frame is used, the layer (d) is never compromised.
The service frame also provides 50mm of extra space for insulation, enhancing energy performance.
The quality of the insulation in this layer is also important.
Since this layer is "inside the house" (see explanation in the next paragraph) it is better to use an insulation that does not contain particles or formaldehyde.
Do your homework and ask your manufacturers.
The vapor barrier is the boundary between the inside of the house and the outside. It shall be completely airtight and the manufacturer should be able to explain how they make it air-tight. Failing to do that means that probably they cannot provide full air-tightness.
Leaking vapor barrier will cause big problems within a few years.
GET THIS RIGHT!
This is the "core" of the wall and every manufacturer offer this more or less correctly.
When it comes to this layer you want to go as wide as you can.
I would recommend 245mm walls for increased energy performance, sound protection, indoor comfort.
The quality of the insulation is also important.
Make sure your manufacturer is informed of the standards and requirements set in your area.
Ans you architect to support the manufacturer when it comes to checking National Norms and local requirements.
Vertical wooden battens provide a space for ventilation and also seal the wind-barrier, giving a robust finish to the wall element.
4.2. Facade Types
Examples of facade materials are:
- wood cladding or boards
- metal cladding or boards
- plastic cladding or boards
- concrete boards
Note that some manufacturers will complete the facade only if the exterior finish material is wood and they will leave to the Client (you) the duty to finish the facade on-site if the material used is not supplied by them.
In general, the more "exotic" is the material you chose, the more project management work you will have to do to get it supplied and installed.
When choosing wood, you will also have to define the type of treatment.
Available options for wood are:
- natural (untreated)
To avoid misunderstandings and to get exactly what you want, it is recommended to include in your price request one or more photos of similar facades.
You can find these images on the web while browsing for terms like "facade cladding", "house facade", ...
Note that some types of materials can only be installed on-site.
Keep in mind that any work executed on-site will cost you more money.
If the price is an issue, ask your manufacturer to suggest the solution for which they can make the best price.
4.3. Roof Types
Roofs can be divided into different categories based on their shape, energy performance, construction.
The shape of the roof can be:
- shed (slope on one side)
- gable (pitched with slope on 2 sides)
- complex (anything with more than 2 slopes)
This page gives an overview of the most common types of roofs.
Keep in mind that the most complex is the roof, the higher its price.
In a building where the attic is cold, insulation is placed right on top of the ceiling of the last rooms and the roof does not need to be insulated.
In a building where the rooms go all the way up to the roof, the roof itself needs to be insulated.
Generally, the shape of the roof determines if the construction can be in elements or not. As a rule of thumb, the most you can build in elements the better (you want to build as much as possible in the factory).
Keep in mind that there is no sense in making elements without insulation, therefore - if you have a cold attic - you will go for roof trusses.
4.4. Foundation Types
- concrete slab (on-site)
- wooden element slab (provided by the Manufacturer)
In both cases, the key concept to keep in mind is that the energy performance of the foundation should be the same (or better) that the energy performance of the roof.
Many make the mistake of thinking the foundation can be plain concrete. Do not make this mistake.
If you are not able to provide a properly insulated concrete slab, ask the manufacturer to provide a wooden element slab.
This solution is the best in terms of Energy performance but it will lift the construction of about 50-80 cm... so you have to consider this carefully if you have height restrictions on your project.
Generally, all concrete works shall be executed by the Client (you) BEFORE the Manufacturer delivers the house.
4.5. Windows and Doors
The most important ones are windows and external doors.
Windows and doors can be made out of three different materials:
Wood is probably the most used material for windows and it comes in a wide range of prices and energy performance.
PVC is the cheapest solution and it offers great Energy performance. However, you should perhaps consider wood or aluminum if you live in a Country where the solar irradiation is high (UV light tends to age the PVC faster).
The use of aluminum is not very common since it is more expensive (for the same energy performance).
Be prepared to discuss extensively windows and doors with your Manufacturer.
5. Technical Systems
- water & sewer
- electricity & data
In general, if the house comes in modules, all the systems are installed in the factory.
If the house comes in elements, the only system that can be installed at the factory is the electricity & data. In most cases, the Manufacturer will install only the plastic pipes and leave the installation of cables to a licensed electrician, on-site.
This system requires good and careful planning since it occupies a considerable volume. All the interference between the ventilation system and the structure of the building (beams, walls, ...) shall be analyzed and optimized.
Good manufacturers will propose you to install in the factories those pipes that go through the vapor barrier of walls and roof elements. All the rest shall be installed on site.
6. Other Components
Although they might not be supplied by the Manufactured, at least their size should be taken into account during design.
The more important additional components are:
- floors (tiles, parquet, ...)
- internal doors
Please note that the amount of components supplied is not indicative of the quality of the service or the quality of the build. In fact, some average Manufacturers try to up their game by offering more services/goods while some very good ones focus only on what they do best: the prefabrication of the house structure.
7. The Process
Knowing all the important stops along the way helps to put together a good planning and to achieve excellent results, within the available budget and time-frame.
7.1. Project Management
Building a house is a process that spans over a couple of years and it involves dozens of people and several companies.
If you plan to buy a prefab house you will have to deal with a lot of technical matter and tons of tiny details. This might need lots of your time.
Many go this way and end up becoming professional Project Managers after the house is completed.
Yes, building a prefab home might change your life :)
2) hire a Project Manager that will handle the Project on your behalf. This is the easier way to go, obviously more expensive.
A good choice for Project Manager could be your Architect... if he/she has the skills and experience to do the job.
Please keep in mind that Project Management is a hands-on job and many Architects are just not a good fit for it.
7.2. Architectural Design
Make sure you pay special attention to tricky things such as fire and sound requirements... remember: you are building a wooden house.
7.3. Price Offer
Make sure you give them exact specifications for what you need and what they should include in terms of delivery and services.
The Price Offer
In case you need, we can help you to figure out if the offers are comparable to and which is the best one.
If you have troubles deciding, you are probably evaluating the wrong metrics. We can help you set the course right... just drop us an email (link above).
for the same price, contract conditions might be very different... so ask for a draft or sample Contract.
From the response of the Manufacturer you will immediately be able to notice a few important things:
- how efficient are they when it comes to paperwork?
- how quick are they in dealing with formal issues?
- do they have procedures in place to handle this kind of request?
Manufacturers that cannot satisfy this request are probably disorganized and stretching out on their capabilities.
If you need a Third Party independent evaluation of the Contract Terms, feel free to ask our help.
7.4. Engineering Design
During this phase, all the details of the building are formalized and represented on paper.
Details like colors and position and layout of technical systems are defined in this phase.
Before signing any drawing make sure you get the technical opinion of your Architect or Engineer.
If something seems missing, ask for it explicitly. Never assume something is "in the price" if not explicitly written.
The Contract to be signed with the Manufacturer (or the Offer) shall state clearly the terms and responsibilities for Engineering Design.
Usually, Manufacturers ask that a local Engineer will approve their design and sign for it.
Generally, delivery is made by trucks.
You are responsible to make sure the trucks can reach your site... so ask the Manufacturer all the info you need to assess that the truck can get to destination (the last stretch of road to your property could be the problem).
The most common delivery is DAP (Incoterm 2010). In case Assembly is provided by the Manufacturer, unloading of trucks is usually included in the price and performed by the Manufacturer at its own risk.
Generally, the Manufacturer is able to complete the Works on-site in less than one month. After that, you can proceed to the interior finish.
In most cases you will be asked to provide:
- a crane to move the elements/modules
- scaffolding for the building (including installation)
- accommodation for the workers of the Manufacturer (usually 4 or more men)
- which materials are supplied and installed
- which materials are supplied but not installed
- which materials are neither supplied nor installed
- how many crane days are foreseen for the assembly
- how many working days (total) are foreseen for the assembly
The Manufacturer shall be able to finish the Works within the estimated time.
7.8. Interior Finishing
Example of interior works, services, materials are:
- interior doors
- floors and tiles
- electricity & data
- water & sewer
Note that the Manufacturer is a supplier and it shall not be confused with a General Contractor.
In many Countries, General Contractors and Real Estate Developers shall give 10 years Guarantee on the houses they sell.
However, Manufacturers cannot are responsible only for the structure of the house and they cannot take responsibility for all the other works and systems.
You shall clarify who is responsible for what and how these responsibilities are assessed in case of need.
8. The Architect
Although you can start planning the house with your own sketch, sooner or later you have to involve a good Architect.
There are multiple reasons why you need an Architect, preferably someone who has experience with building prefab wooden houses.
Here a list of a few reasons that make the Architect so important:
- someone has to guide you through what you can do and what you cannot do (architecturally speaking)
- Manufacturers take more seriously those projects with good architectural drawings, hence your chance of getting a complete price offer is higher if you involve an Architect
- the Architect can help you to evaluate and comment the design work of the Manufacturer
- the Architect can handle for you the relationship with the Manufacturer
- believe it or not, there are not many Architects capable of designing a house ready for manufacturing. Manufacturers appreciate projects that are optimized for factory production and they will treat yours with priority if the design is good.
Given the reasons above, it makes sense to choose the Architect at a very early stage.
In any case, DO NOT:
- ask the Manufacturer to price multiple variations of the same project. Your Architect should be able to guide you through the selection of components and solutions, providing a ballpark estimate of what is cheaper and what is more expensive. Manufacturers are busy. Ask them to price only the version you really intend to build.
9. The Manufacturer
Choosing the Manufacturer for the production of your house is perhaps the bigger step you have to take in the entire process.
Do not postpone this decision: it pays off to choose a Producer at an early stage.
Many drag this decision far too long and end up rushing the design a product to meet the deadlines of their project schedule. This is a very bad way to build your home (or any building).
What drives people to procrastinate on this decision is usually the price. They fear to pick a Manufacturer that is too expensive and they fear to miss out on "the best price".
Here are a few things to consider, to help you see that the price of the house set does not matter that much:
- unforeseen on-site due to lack of preparation/logistic can cost thousands EUR. A good manufacturer can help you with planning and this can easily justify a higher price (and cover for that 5% above).
- in a construction project, communication is the most important thing you should look at. You should always try to pick the Manufacturer with the Team you "feel" a connection with. It is important to focus on the Project Management Team and not on the Sales Team.
Ask the Manufacturer to meet the Project Manager and his Team, or at least to speak to them. These are the people you'll be dealing with for the entire project and you shall be able to have pleasant and crystal clear communication with them.
Any misunderstanding will cost money, time... and headaches.
On top of excellent communication make sure your Manufacturer does:
- use ONLY materials and components that are CE marked (failure to do so indicates poor standards and willingness to cut on quality in favor of profit)
- have ISO certifications (at least 9001)
- have a plan to make your house airtight. This is one of the biggest challenges and asking this question can show you the technical skill of the Manufacturers' Team.
If you ask this question to different Manufacturers you will notice their "reaction" to very technical questions can be quite different.
NOTE: your Architect can help you to evaluate the answers.
10. Getting Started
No need. A journey of a thousand mile begins with one step.
Here a short roadmap so you do not get lost:
1) Get your sketch done (SketchUp is great for this) or put your requirements and need on paper.
2) Get a good Architect
3) figure out the details of the building (which kind of windows, which kind of facade, which kind of roof, ...)
4) ask for at least 3 price offers
5) interview the Project Management Teams
6) pick your Manufacturer (not based on price only!!!)
I'd also recommend you get in touch with us... we might be able to support you.