Fundament til dit havehus

Et fundament til en bygning du rent faktisk opholder dig i

Et havehus er et rum, ikke et redskabsskur. IBRAN-gitre giver et fast, plant og frit-drænende fundament, der holder gulvet tørt og bygningen i lod – og som fremstår som en bevidst del af haven frem for en betonplade.

Hvorfor fundamentet betyder mere end selve bygningen

Et havehus stiller større krav til sit fundament end nogen anden havebygning, fordi det handler om, hvad der foregår indeni.

Folk sidder der i timevis. Der er tæpper, puder, bøger, en sofa, sommetider et skrivebord og en laptop, ofte strøm og belysning. Alt det er langt mere følsomt over for fugt end en plæneklipper. Et skurgulv med lidt fugt nedefra er stadig et skur. Et havehus med lidt fugt nedefra lugter af mug inden for en sæson og ødelægger bløde møbler inden for to.

Det bliver også set. Et havehus placeres typisk som et blikkfang for enden af haven, så fundamentet er synligt fra huset hele året. En grå betonafdækning signalerer byggeplads; et rent grusfelt signalerer haveanlæg.

Og det bærer mere vægt, end folk forventer. Møbler, beboere, en brændeovn, en vandtønde i hjørnet, sommetider en lille terrasse. Ujævnt fordelt over et fundament, der sætter sig ujævnt, og bygningen mister langsomt sin retning.

Et armeret gitter håndterer alle tre udfordringer: indespærret skærver giver en stiv platform, der ikke sætter sig i pletter; overfladen forbliver fuldt permeabel, så fugt dræner væk og luft bevæger sig under gulvet; og grus fremstår som en bevidst del af haven frem for et fremmedelement.

Hvor dette fungerer godt

Havehuse og haverum
Hjemmekontorer og atelierer
Tømmerhytter og chalets
Pavilloner, pergola og havebarer
Omgivelser til boblebad og spa
Terrassearealer og hævede platforme
Adgangsstier og tærskler
Erstatning af en fejlslagen plade eller belægning

Overblik

Bærelag	100-150mm komprimeret stabilgrus, mere ved større hytter eller tungt indhold
Fyldmateriale	6-14mm sorteret blanding, kantet og rent, fyldt i niveau med celletoppe
Samlet udgravning	Ca. 140-190mm afhængigt af gitterdybde og bærelag
Udseende	Kan afsluttes med dekorativt tilslag tilpasset haven
Dræning	Fuldt permeabelt. Ingen stående vand mod bygningen, intet fugtigt gulv
Tilgængelighed	Tæt pakket sorteret fyld giver en fast adgang egnet til hjulbaseret færdsel
Designlevetid	25 år, forudsat dokumenteret udførelse
Materiale	100% genanvendt polypropylen, bæredygtigt fremstillet i EU

Sådan holder du indersiden tør

Det er her, forskellen opstår mellem et havehus, der er behageligt i marts, og et der kun kan bruges i juli.

Fugt trænger ind i et haverum nedefra langt oftere end gennem taget. Fugt stiger op fra jorden, kondenserer mod et koldt gulv og har ingen steder at slippe ud – og det første tegn er som regel en lugt frem for en plet.

Et permeabelt fundament bryder den cyklus. Vand dræner ned gennem skærverne i stedet for at stagnere under bygningen, og luft bevæger sig gennem hulrummet under gulvet frem for at stagnere i det.

Byg på løsholter, så der er et klart ventileret mellemrum; lad fundamentet strække sig ud over væggene, så tagvand lander på sten; og hold beplantning klippet tilbage fra siderne. Hvor bygningen er isoleret og bruges hele året, er en fugtspærre i gulvopbygningen værd at drøfte med producenten – jo bedre isoleret rummet er, jo vigtigere er det, at fugt ikke kan trænge ind nedefra.

Gør fundamentet til en del af haven

Dette afsnit eksisterer ikke for et skur, og det er her et grusfundament tjener sig hjem visuelt.

Lad fundamentet strække sig godt ud over bygningens fodaftryk, og det ophører med at være et fundament og bliver en ramme: et grusareal bygningen sidder i, bredt nok til en stol uden for døren, et bord, et par urtepotter. Det fremstår intentionelt og giver dig et tørt sted at stå, der ikke er plæne.

Dekorativt tilslag fungerer perfekt her, så overfladen kan matches til eksisterende stier, beplantning eller huset. Lokalt sten ser som regel bedre ud end importeret og koster mindre at levere.

Hvor havehuset støder op til en terrasse, føres gitterfundamentet helt hen til den og afsluttes i flugt, så der hverken er et trin eller en sprække, der samler blade. Hvor det møder plænen, giver en kantafgrænsning en ren linje og fungerer samtidig som klippekant.

Hvilken gitterdybde?

Tallet på et gitter er en beslutning om, hvor dybt det indespærrede stenlag er. Havehuse er tungere end skure og er beboede, så vælg lidt dybere end du ville til et opbevaringsrum.

IBRAN®-X40 er det naturlige valg til de fleste havehuse og haverum: tilstrækkelig dybde til bygningen, møblerne og menneskene i den.
IBRAN®-X30 til mindre konstruktioner, pavilloner og pergola, eller hvor færdige niveauer skal matche en eksisterende terrasse eller tærskel nøje.
IBRAN®-X50 til store tømmerhytter, bygninger med brændeovn eller tungt indvendigt udstyr, eller hvor et boblebad indgår.

Boblebade fortjener særlig opmærksomhed: fyldt og i brug er de langt tungere end noget andet, der sandsynligvis placeres i en have. Kontrollér karrets angivne belastede vægt og dimensionér bærelaget specifikt herefter.

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Recommended for this project

Plastic Shed Base Grids

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How it goes in

Check the manufacturer's base requirements first. Larger cabins often specify a minimum base size, a bearer spacing or a particular level tolerance, and it is easier to build to it than to discover it on delivery day.
Mark out the base generously: at least 100mm beyond the building on every side as a minimum, and considerably more where you want a usable apron.
Clear turf, roots and soft soil to firm ground, and check the ground falls away from the building position.
Excavate to your total depth: sub-base plus grid depth, typically 140-190mm.
Lay a woven geotextile across the dig, lapping joins by at least 300mm and taking it up the sides.
Add the sub-base and compact it in layers. 100-150mm of MOT, compacted properly, is what stops an occupied building settling unevenly over the years.
Blind with a thin layer of grit sand and screed it level. Check with a straight edge and spirit level in both directions, and check the diagonals of the marked area match.
Push-fit the grids together, cutting the perimeter to line with a hand saw.
Fill the cells with a 6-14mm graded blend, level with the cell tops, brushing in so no cell is left hollow.
Set the building on bearers, check square and level, then fix down.

Full step-by-step detail is in our installation guides.

Services and the things you forget

A summerhouse is usually the one garden building that ends up with power, and occasionally water, and both are considerably easier to deal with before the base goes down.

Run a duct under the base while it is open, even if you have no immediate plans for electrics. An empty conduit costs almost nothing at this stage and saves lifting a finished surface later, which is the point at which most people give up and run a cable across the lawn instead.

Think about where the water goes, too. A summerhouse roof concentrates runoff at its eaves or downpipe, and a permeable base handles ordinary rainfall comfortably but not a downpipe discharging in one spot for years. Direct it into a butt, a soakaway, or at least away from the corner of the building.

Any electrical work should be done by a qualified electrician and will usually need to comply with Part P.

Thresholds, steps and access

A summerhouse is entered and left constantly, and the threshold is where a base either works or annoys you daily.

Take the base out further on the door side than anywhere else, so there is a proper standing area rather than a step straight onto grass. If the building has a veranda or decking, run the base underneath and beyond it.

Where the garden room is used year round or by anyone with limited mobility, a densely packed graded fill gives a firm surface that takes a wheelchair or a walking frame, which loose gravel does not. Keep the finished level flush with the threshold rather than leaving a lip, and run the approach path in the same surface so there is no transition to catch a wheel.

Sloping gardens

Summerhouses are often sited at the end of a garden, which is frequently the part that is not flat.

For a gentle slope, dig into the high side rather than building up the low side: material you have added is always less stable than ground you have not disturbed, and an occupied building will find any weakness over time.

On a steeper slope you will need a retained edge, and it is worth getting that right rather than improvising, because it is holding back the ground your building sits on. Where the drop is significant, consider whether a deck platform is a better answer than a very deep cut, and take advice on anything structural.

Get it right first time

The one thing worth knowing: build the base bigger than you think you need.

Almost nobody regrets a generous base. Plenty of people regret a tight one, and it is the single most common thing to wish you had done differently, because it is the one thing that cannot be changed once the building is up and the planting has gone in around it.

An extra half metre of gravel apron costs very little at construction and completely changes how the building is used: a chair outside the door, a table in the sun, somewhere dry to stand in March, room to get round the outside to treat the timber. Stop the base at the walls and you have a building you go inside; extend it and you have a place in the garden.

Ask our engineer

Questions about depths, base sizing, sloping ground or hot tub loading? Ask below, or get in touch directly.

Common Questions

Things that frequently come up when carrying out this project.

Is a gravel grid base suitable for a summerhouse or garden room?

Yes, and it suits an occupied building particularly well. Confined stone gives a rigid platform that does not settle in patches under furniture and people, and the surface stays fully permeable so moisture drains away rather than collecting under the floor.

It also finishes as a considered part of the garden rather than a concrete apron in view of the house.

How do I stop a garden room getting damp?

Damp usually comes from underneath rather than through the roof: moisture rises from the ground, condenses against a cold floor and has nowhere to escape. A permeable base lets water drain down through the stone instead of sitting under the building, and bearers keep a ventilated gap so air moves through.

Extend the base beyond the walls so roof runoff lands on stone, and keep planting cut back from the sides.

How deep should a summerhouse base be?

Around 140mm to 190mm in total: 100mm to 150mm of compacted MOT sub-base plus the grid depth, with more for larger cabins or heavy contents.

Compact the sub-base in layers rather than tipping and raking it, because that is what stops an occupied building settling unevenly over the years.

Which grid depth do I need for a summerhouse?

The 40mm grid is the sensible default for most summerhouses and garden rooms: enough depth for the building, the furniture and the people in it. Use 30mm for smaller structures, gazebos and pergolas, or where levels must match an existing patio.

Use 50mm for large log cabins, buildings with a wood burner or heavy fit-out, or where a hot tub is involved.

How big should the base be?

At least 100mm beyond the building on every side as a minimum, and considerably more where you want a usable apron. An extra half metre of gravel costs very little at construction and completely changes how the building is used: somewhere to put a chair, a table, or just somewhere dry to stand.

It is the most common thing people wish they had done, and it cannot be changed once the building is up.

Can I run electrics to the summerhouse?

Run a duct under the base while it is open, even if you have no immediate plans for power. An empty conduit costs almost nothing at that stage and saves lifting a finished surface later.

Any electrical work should be carried out by a qualified electrician and will usually need to comply with Part P.

Will a gravel base take a hot tub?

It can, but design for it specifically. Filled and occupied, a hot tub is far heavier than anything else likely to sit in a garden, so check the manufacturer's stated loaded weight and build the sub-base and grid depth against that figure rather than against the building.

The 50mm grid with a deeper compacted sub-base is the usual answer.

Is the base wheelchair accessible?

A densely packed graded fill gives a firm surface that takes a wheelchair, walking frame or pushchair, which loose gravel does not.

Keep the finished level flush with the threshold rather than leaving a lip, and run the approach path in the same surface so there is no transition to catch a wheel.

What gravel should I finish it with?

A 6mm to 14mm graded blend, angular and clean, filled level with the cell tops. Decorative aggregate works well here so the surface can be matched to existing paths, planting or the house, and local stone usually looks better than imported and costs less to deliver.

Avoid rounded shingle, which shifts underfoot, and anything with fines, which binds and stops the base draining.

Can I build a summerhouse base on a slope?

Yes. For a gentle slope, dig into the high side rather than building up the low side, since added material is always less stable than undisturbed ground and an occupied building will find any weakness.

On a steeper slope you will need a properly retained edge, and where the drop is significant it is worth considering whether a deck platform is a better answer and taking advice on anything structural.