What is in a mobile home?

General Element

Requirements

Possible issues

Base or Slab.

A reinforced concrete raft on which the home will be positioned.  The position of the slab should allow the home when sited to be at least 6 metres from an adjacent home and 2 metres from a road.

Constructed of reinforced concrete.

Some older sites used aggregates for the bases. Well compacted and of the correct size, this has performed well enough.  However, be suspicious if the plot you are considering is not made of concrete and avoid this at all costs.

Base should be generally level.  A Slight run is permissible to allow for water run-off should any find its way on to the slab when the home is in positioned.  Water should not be allowed to stand under the home.

A base which is too far out of level, will make the home difficult to level and support.  This could result in support stands being installed incorrectly damaging the underneath of the home and make the home unstable. 

Erection of the brick skirt, if any, will be difficult to construct.

The slab should be at least 150mm thick and be cast on a prepared foundation of compacted aggregates.  The NCC suggest the preparation is in accordance with the nature of the ground. Difficult to check but asking the questions about the site is sensible.

The slab has been constructed on made up ground which has not been correctly filled.  Subsequent subsidence or heave may occur.

The slab is not reinforced.

The slab should be higher than the surrounding ground which should slope gently away from it ensuring water cannot run on to it.

The slab is visibly lower than the ground surrounding it.

The slab should have a ground water drain installed around the periphery which should be connected to a drainage system or soakaway.

No proper drainage is provided with the possibility of water undermining the slab over time.

The dimensions should be the same size as the home which is standing on it.

All the support jacks on which the home sits need to be well inside the perimeter of the slab.

The slab should not be so large as to allow water which runs off the sides of the home to stand on the surface.

Chassis

A steel welded and protected fabrication on which the home is constructed.  It is the backbone of the home and the main provider of structural integrity.  The chassis also provides the wheel and axles which are used to move the home, and which make the home legally a Caravan for the purposes of the mobile homes act.

The failure of the chassis will condemn the home.

The chassis needs to be robust enough to support the weight of the home and remain level and sound for the claimed life of the structure.

The correct positioning of the support jacks when sited is essential to ensure the home remains securely positioned.

When transported the home may be left for periods of time without adequate support resulting in damage to the internal structure which later in the life of the home could appear as structural failures.

The protective coating should, take into consideration the location of the home, be undamaged when sited and last for the time stated in the specification before any remedial work is required.

Poor handling and subsequent scuffs and scrapes will result in premature corrosion which in a coastal location will cause major damage in a short time.

The wheel and tyres need to be in good serviceable order for the whole of the home’s life.  The tow bars should also be in good order.

It is possible that if the wheels and tyres are removed and do not stay with the home claims could be made that it is no longer a caravan and therefore it no longer benefits from the protection given by the mobile homes act with serious implications.

Any box sections (hollow components) need to be plugged to prevent internal corrosion for forming.

Box sections are not necessarily internally painted and are subject to internal rusting as a result.

Structure

Floor

Timber floor joists are attached to the chassis with screws or bolts.

Flooring grade sheet is fixed over the joists.

Insulation and a vapour permeable membrane is placed under the floor to completely infill the gaps between the joists.

The materials of construction should be to BS3632:2015 and the insulation should also meet the requirements for thermal conductivity.

This is difficult to assess and it is where a surveyor should be consulted.

Insufficient insulation is common requiring supplementary insulation being fitted later at the owner’s cost. 

The insulation also protects the water pipes most often installed beneath the floor.  Poor insulation will lead to frozen pipes.

Framing

The elevations and internal walls are formed from timber which should be treated against rot and insect infestation.

External walls are generally 100mm deep whilst external walls tend to be160mm in depth.

The precise design of the home will be determined by a particular manufacturer but the placement of internal walls together with the external timbers and roof trusses all contribute to the strength and stability of the structure.

The materials of construction should be to BS3632:2015 and the insulation should also meet the requirements for thermal conductivity.

The problem here is that unless you visit the home manufacturers factory and see first-hand how the homes are made, it is difficult to establish otherwise.

Again, this is where a surveyor will help.

Walls

Modern homes can have a variety of materials forming the walls.

External walls can still be made of plywood which is poor at resisting moisture.

Many homes have had their external walls replaced following water ingress through damaged render.

Many modern homes are now clad using a moisture resistant material such as magnesium board. 

This is much more resistant to water ingress but still any damp is fatal to a park home.  The external walls should be filled with the correct insulation. 

Internal walls are mostly plaster board with some sections being formed with plywood where addition strength might be desirable.  This could be where wall tiles are being fixed or where sections need additional stiffness particularly during transportation.

The materials of construction should be to BS3632:2015 and the insulation should also meet the requirements for thermal conductivity and fire spread.

Again, this is where a surveyor will help.

Tip.  External boarding can often be seen if the home is viewed from underneath just behind the drip rail.

It is not uncommon for inadequate insulation to be found in outside walls; in some cases, there has been found to be no insulation at all!

An early indication of missing or inadequate insulation is the appearance of damp patches which form on the internal walls, particularly in the colder months.  A persistent damp patch will certainly be caused by this.

Roof

The structure of the roof is normally timber trusses.  There are generally many more trusses than in a conventional house these being of lighter construction.

The roof space should be ventilated and well insulated.

Mobile homes use light- weight steel tiles.  These come with a generous 40- year guarantee but like anything else the warranty is only valid if the tiles are fitted correctly and are undamaged. Other conditions apply.

Badly constructed roofs and tiling leading to leaks is not an uncommon problem with park homes.

Park home designers take great delight in constructing faux features such as chimneys and gables that have no purpose but add complication to the roof construction and invite leaks.

The materials of construction should be to BS3632:2015 and the insulation should also meet the requirements for thermal conductivity and fire spread

There seems to be a huge variation in the way in which roof trusses are made.

One home I have seen was formed of timber with plywood joint plates held together with oversized nails most of which had missed the timbers.

Another much more professionally built home clearly had trusses made in a truss press with proprietary joint plates. 

Whilst either method might seem to be adequate, it is always a good indicator as to the overall construction quality when one sees these extremes.

A surveyor will assist here.

An overly ornate and complicated roof structure should be avoided.

Windows and doors

As one might expect these are generally UPVC though some manufacturers do offer wood.

Many manufacturers make window in house.  While this might seem advantageous the incidence of badly fitting frames and sashes is all too common.

Badly fitted frames will allow water ingress into the external wall boarding.

External render.

This is an area that can cause major confusion and issues.

At present the most common coating used on mobile homes is Resitex and with the attendant paint system, Resifine are in the majority.

Mapei coatings are now gaining popularity.

So, what are these coatings?

We need to make the home watertight and protect it from water damage principally.

Resitex is a textured water based viscous render that forms a water-resistant film over the substrate onto which it is applied.  It is mineralised and so gives the impression of a sand-based render.

Resitex seems to be a similar material but without the minerals so acts more like a plastic coloured coating.

Re coating is required after two years and then every three years thereafter.

In the meantime, GoldShield require checking of the coating every three months as cracks can occur and let water under the coating causing the coating to delaminate and the cladding underneath to rot.

So much for low maintenance mobile homes!

Mapei however guarantee their coatings for 10 years after which a coat of paint revalidates the guarantee for another ten years.

Building works

Skirting

This is normally constructed from brickwork.

The skirt provides weather protection for the chassis, rolling gear and services under the home.  It also gives a degree of protection preventing freezing pipes through this is not a substitute for effective lagging.  Mostly you will be told the skirt is to improve the look of the home.  Adequate ventilation is also required through the fitting of airbricks in the skirt to coincide with each room within the home.

Little notice is taken of the codes of practice and seldom will there be a damp proof course.  The wall will often be either touching or close to the home structure.  Both these faults will increase the likely hood that moisture will penetrate the fabric causing rot and mould.  Clearly undesirable in any home but disastrous for a park home.  Such a problem is likely to void any insurance you may have.

Patio and hard landscaping

Much the same as the skirt, these structures should not be allowed to touch any part of the home.  If built, a raised patio needs to be ventilated to avoid the transfer of damp into the home structure. Entrance steps and other building work need to be kept clear.

Check the structures are not touching.  Make sure there is enough gap to ensure damp cannot penetrate, access can be gained for inspection and all parts of the structure can be accessed for the required painting.

Planting

Any existing or intended planting should not touch the home.  It is recommended that all planting should be kept at least 300mm from the structure.

Check that any planting is clear of the home.  Also ensure that when watering plant of when raining water cannot run onto the structure.

One aspect that is always overlooked is the damage that is caused to the home by the builders erecting the hard landscaping who will not appreciate the significance of avoiding this.   When placing bricks the paint can easily be damaged and as now the chassis is obscured you will never know the steel work is exposed to the air allowing corrosion to occur.