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Structural Insulated Panels
Structural Insulated Panels are pre-engineering building systems. This article explains what they are, how they are made and their properties.
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Structural Insulated Panels are pre-engineering building systems, manufactured in a controlled environment and shipped to site ready for erection.
The Structural Insulated Panels consist of an inner ridged insulating core of Expanded Polystyrene (EPS) and two outer skins of oriented strand board (OSB), this works by sandwiching the solid core of insulation between two skins of OSB board.
When engineered and assembled, a structure built with SIPs needs no frame to support it. The panels form the strength, insulation and structural envelope of the building, and are also used for the roof and internal load bearing walls.
Where to use SIPs
SIP panels are used effectively in the construction of:
- Housing
- Light commercial and industrial buildings
- Extensions
- Roof Panels
- Barns / Conversions
- Garden and Office cabins
- Cladding envelope for oak frame Buildings
SIPs construction replaces traditional timber frame, brick built houses and pre-fabricated type buildings, with the added benefit that SIP roof applications, means that no roof trusses are required, gaining an additional room in the roof space.
How is it made?
Stage 1
The Expanded Polystyrene (EPS) is passed through an electrically driven glue spreader. The P.V.A. glue used is water based and is solvent free.
Stage 2
Expanded polystyrene is then laid onto a sheet of oriented strand board using a lay-up table system.
Stage 3
A second sheet of OSB is then applied to form the structural sandwich.
Stage 4
This sandwich then continues into a pneumatic laminating press by means of electric motors. The panels are then pressed for a specified time under a specified pressure to ensure satisfactory bond results.
All materials are ordered to size to eliminate the waste during the pressing process.
Joist options with a SIP house
Trus Joist (TJI) Floor System
The floor systems used in a SIP house is integral to the structural package. The standard Trus Joist (TJI) which may also be referred to as an I-Beam or I-Joist, because of it's 'I' shape in cross-section, is used as standard in a build it green sip house. These joists are manufactured at a low and uniform moisture content to avoid the splitting, bowing and twisting, so commonly associated with traditional solid timber joists. This is why Build It Green buildings are free from squeaky floors and cracked walls.
TJI joists also offer many more benefits. They are much lighter than solid timber joists and can be installed in a fraction of the time. Available in long lengths, they speed up installation and increase floor rigidity by eliminating laps over beams and walls.
Independent research has shown that TJI joist system is a cost-effective alternative to conventional floor framing, once you take into account the speed and ease of installation. Due to their design, TJI joists also make efficient use of precious timber resources.
Ecojoist Floor System
Occasionally, some applications may require a different joist system to be specified, whether it be the customers choice or a requirement due to the design.
Ecojoists offer longer spanning capabilities than a TJI joist system and have different characteristics.
Ecojoist beams consist of parallel stress graded timber flanges joined together with engineered V shaped galvanised steel of 8" and 9" webs. The webs are fixed to the flanges via the nail-plated zones top and bottom.
Ecojoist sizes are compatible with those of solid joists and TJI joists, so there is no need for expensive drawing changes. They are made to measure, no site wastage and quicker to install.
Further advantages include:
- Wide surfaces enable easy OSB and plasterboard fixing
- Open web system means there is no need to notch or drill for pipes and cables.
- Additional services can then be installed with minimum disruption.
- It is 40% lighter than equivalent solid joists, therefore an Ecojoist easier to handle and manoeuvre on site.
Mechanical Ventilation Heat Recovery (MVHR)
Mechanical ventilation with heat recovery (MVHR) or Heating ventilation and cooling systems (HVAC) are a sensible and beneficial addition to a SIP Building System. The Building Regulations encourage architects and builders to 'Build tight, ventilate right', therefore, introducing controlled ventilation is considered good practice.
Mechanical Ventilation Heat Recovery (MVHR) Systems bring fresh air into the home or building and exhaust the moisture laden or stale air to the outside. Often they can be combined with filter systems or other fresh air devices. Not only is ventilation practical, but a requirement in airtight constructions.
The diagram shows airflow through a typical application. It can be seen that as well as extracting pollution and moisture the unit provides fresh air from outside. Importantly as the fresh air is warmed by the heat exchanger, the relative humidity is lowered far below the level required for a dust mite infestation.
In this way all MVHR systems constantly refresh the internal environment replacing stale moist air with fresh, drier air. This means that a Build It Green SIP home provides a more comfortable and healthier living environment.
The Heat Exchanger Principle
At the heart of the MVHR System is a unique state-of-the-art lightweight heat exchanger which returns up to *70-80% of the heat in the outgoing stale air stream. This valuable heat energy is transferred to the incoming fresh air supply. The airstreams do not mix and there is no cross-contamination.
How do you install the wiring?
Where possible we run wiring through internal studs partitioning walls. However, where wiring has to be run up external walls there are two methods with which it can be done:
Option 1 - Timber Battens Fix 10mm timber battens at 600-mm centres and install the wiring between them along with an IEE approved metal guard. Then mechanically fix 9.5mm or 12.5mm plasterboard over the battens. (See next section for requirements for fixing surface mounted pipes when using a single layer of plasterboard on a 10mm batten).
Option 2 - Double Layer Plasterboard. Mechanically fix the first layer of 9.5mm or 12.5mm plasterboard to the SIP wall or roof panels at 300 mm centres using plasterboard screw fixings, leaving a suitable void between the sheets of plasterboard where the wiring is to be situated.
Having installed the wiring along with an IEE approved metal guard; you then mechanically fix the second layer of plasterboard over the first layer using plasterboard screw fixings at 300-mm centres.
Double layer plasterboard is the preferred option as the wall and roof panels have a very solid and robust characteristic unlike some timber frame walls, which often sound hollow and flimsy. A further benefit of the double layered plaster board is a class 0 fire rating is achieved (to find out more about this see fire rating of a sip house).
How do you install plumbing?
Plumbing can is installed in much the same way as the electrical services and adopts the same principles used in and other construction method.
The Build It Green Building System can use the same ground floor system as any other system and consequently the ground floor plumbing depends on the floor type.
At first floor level, we use TJI joists, so the pipes can be installed in the same way as any other system.
When plumbing has to be run up the wall, where possible we run pipes through internal studs partitioning walls. If this is not possible, we would consider 'boxing-out a small section to accommodate the pipe work.
Surface mounted pipe work can also be hidden within double layer plasterboard.
Fixing Radiators, and other heavy flush items onto a Build It Green Wall, which has used double layer plasterboard means there are no restrictions on where they can be situated. Also there is no extra labour involved, unlike timber frame where timber cross noggins have to be installed for fixing units such as radiators.
Interior Finishes
When you first walk into a SIP building after the shell has been erected, the first thing you notice is the continuous surface of the oriented strand board (OSB) facing.
Unfortunately, you can not just paint this surface because all buildings require a fire-resistant surface on interior walls.
The standard finish for interior walls and ceilings is dry lining using one layer of 12.5mm plasterboard and to fire-tape the joints. This achieves a class one fire rating. The optimum class 0 fire rating is achieved if two layers of plasterboard are attached.
The interior finishes in a SIP house can be the same as in any other house, the picture below shows painted walls in a neutral colour scheme.
Exterior Finishes
With many exterior wall finishes available, a SIP house looks no different from the outside than its surrounding neighbours.
The variety of available wall finishes is vast and will be dictated as much by the style of the building as the customer's budget.
Exterior wall finishes start after the SIP shell has been erected and the waterproof breather membrane is fitted.
Masonry Exterior Finishes
Stone and brick are excellent wall finishes for a SIP building, the inert nature of the SIP panels prevents the building from suffering any shrinkage that could distort walls and cause joint cracks in the masonry.
For Brick and stone a concrete ledge needs to be included in the foundation design.
Render Exterior Finishes
Render finishes also known as Stucco, are highly compatible with the SIP system.
Commonly used is a light weight polymer modified render system, this is applied over a cementitious board or expended metal sheets fixed to treated softwood counter battens that are attached to the SIP walls.
The multi-coat render system can be applied by brush, trowel or spray. The finish either has colour in it or it can be painted afterward.
Weather Boarding Exterior Finishes
Weather boarding is available in a variety of types and has been used on many SIP buildings.
One of the most compatible boarding material used with SIPs is cedar, this timber boarding is beautiful to look at and is very durable. It is fixed to treated softwood counter battens that are attached to the SIP walls.
As an alternative to timber cladding, a light weight cement fibre weather board is also available. This is a man made product, designed to replicate the visual appeal of the original. Weatherboard can be supplied in a Natural finish or in one of a range of 6 factory applied colours.
SIPs Technical data
Standard SIP panel dimensions available are:
- 2400mm (H) x 1200mm (W)
- 4800mm (H) x 1200mm (W)
Panel Weights
- 2400mm - 42kg
- 4800mm - 84kg
Panel Thickness
- 117mm (2 x 11mm OSB + 95mm rigid EPS insulation core)
- 167mm (2 x 11mm OSB + 145mm rigid EPS insulation core)
Fire Performance
When lined internally with 12.5mm plasterboard the panels achieve a Class 1 fire rating.
A Class 0 fire rating is achieved if two layers of plasterboard are fixed.
In common with all other forms of construction in the UK, Structural Insulated Panels has to meet all UK Building Regulations.
Panels have passed the rigorous fire endurance tests. Their solid-core construction eliminates the "chimney effect" that causes fires to spread rapidly through hollow conventional-built walls. The super-bonding, insulating foam we use is non-toxic and chemically inert.
Thermal Performance
- 95mm core panels achieve a U value of 0.28 W/m2K
- 145mm core panels achieve a U value of 0.22 W/m2K
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