Laravel 5.2 foreign key constraint fails

I am getting the following error when I try to save a new property:

SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (lightning.residentials, CONSTRAINT residentials_residential_type_id_foreign FOREIGN KEY (residential_type_id) REFERENCES residential_types (id)) (SQL: insert into residentials (furnished, rooms, rent, property_id, updated_at, created_at) values (1, 1, 100, 17, 2016-07-06 23:32:59, 2016-07-06 23:32:59))

I cant see why.

Db schema

The Property model:

   protected $table = 'properties';
/**
 * The attributes that are mass assignable.
 *
 * @var array
 */
protected $fillable = [
    'user_id', 'is_for_sale','available','title', 'description','price'
];

public function user()
{
    return $this->belongsTo('App\User');
}


public function Residential()
{
    return $this->hasOne('App\Residential');
}

/**
 * The Addresses that belong to the properties.
 */
public function addresses()
{
    return $this->belongsToMany('App\Address');
}

address model

 /**
 * The attributes that are mass assignable.
 *
 * @var array
 */
protected $fillable = [
    'building_name', 'street_number', 'street_name', 'town', 'county', 'postcode','is_deleted'
];



/**
 * The Users that belong to the Address.
 */
public function user()
{
    return $this->belongsToMany('App\User');
}

/**
 * The Users that belong to the Address.
 */
public function organisation()
{
    return $this->belongsToMany('App\Organisation');
}

/**
 * The Users that belong to the Address.
 */
public function Property()
{
    return $this->belongsToMany('App\Properties');
}

The residential model:

protected $table = 'residentials';

/**
 * The attributes that are mass assignable.
 *
 * @var array
 */
protected $fillable = [
    'property_id', 'residential_type_id','furnished','rooms','rent'
];

public function Property()
{
    return $this->belongsTo('App\Property');
}


public function Residential_Type()
{
    return $this->belongsTo('App\Residential_types');
}

The residential_type model

 // Define table name
protected $table = 'residential_types';

protected $fillable = [
    'residential_type'
];


/**
 *
 */
public function Residential()
{
    return $this->hasMany('App\Residential', 'residential_type_id');
}

My controller function where I try to save a property along with the fields in the related residential table but I get the error above. The property and address saves correctly just fails when it comes to the residential.

  $property = new Property([
        'user_id' => $user->id,
        'is_for_sale' => $request['listing_type'],
        'available' => $request['available'],
        'title' => $request['title'],
        'description' => $request['description'],
        'price' => $request['price'],
    ]);

    $property->save();

    //save address and related to property
    $address = new Address([
        'building_name' => $request['building_name'],
        'street_number' => $request['street_number'],
        'street_name' => $request['street_name'],
        'town' => $request['town'],
        'county' => $request['county'],
        'postcode' => $request['postcode'],
    ]);
    $property->addresses()->save($address);

    //save property and related to residential
    $residential = new Residential([
        'furnished' => $request['furnished'],
        'rooms' => $request['bedrooms'],
        'rent' => $request['price'],
    ]);


    $residential_type = new Residential_Types([
        'residential_type' => $request['property_type'],
    ]);

    $residential_type->save();


    $property->Residential()->save($residential);

    $residential->Residential_Type()->save($residential_type);


    return view('renting');

via Chebli Mohamed